Oilfield chemical tracer material

Abstract

An oilfield tracer material comprising: a polymer matrix; and an oilfield chemical tracer, wherein the oilfield chemical tracer is an oil tracer, wherein the oilfield tracer material comprises between 5% and 25% by weight of the oil tracer, and wherein the oil tracer is substantially homogeneously dispersed throughout the polymer matrix at a molecular level.

Description

[0001] OILFIELD CHEMICAL TRACER MATERIAL

[0002] Field of the Invention

[0003] The present specification relates to an oilfield chemical tracer material for controlled release of oilfield chemical tracer within a hydrocarbon reservoir, well, or wellbore. The present specification also relates to a method of manufacturing such an oilfield chemical tracer material, polymer articles formed of the oilfield chemical tracer material, and methods of oilfield tracing using the oilfield chemical tracer material.

[0004] Background of the Invention

[0005] It is common practice to use oilfield chemical tracers for monitoring of hydrocarbon reservoirs. Optimal oil and gas production from the reservoir depends upon reliable knowledge of the reservoir characteristics. Traditional methods for reservoir monitoring include seismic log interpretation, well pressure testing, production fluid analysis, production history matching, and interwell, near wellbore, and wellbore tracer techniques. Due to the complexity of the reservoir, all information available is valuable in order to give the operator the best possible knowledge about the dynamics in the reservoir. One common secondary oil recovery process is fluid injection (e.g., water or gas injection) in dedicated injection wells. The fluid may travel in different layers and sweep (flow across) different areas in the reservoir. Monitoring of the production of this fluid in different zones in the well is important to design a production program that improves the sweep efficiency and thereby increase oil recovery. Mixing of injection fluid and formation water originally present in the reservoir may cause supersaturated solutions leading to precipitation of particles (scale) in either the reservoir near well zone or in the production tubing. By knowing which zone or zones contribute to water production, action can be taken to reduce the effect of scaling and thereby maintain productivity.

[0006] The use of tracers to obtain information about a hydrocarbon reservoir and / or about what is taking place therein has been practiced for several decades and has been described in numerous documents. Tracers have primarily been used to monitor fluid paths and velocities. More than one tracer substance can be used concurrently. For instance, U.S. Pat. No. 5,892,147 discloses a procedure in which different tracers are placed at respective locations along the length of a well penetrating a reservoir. The tracers are placed at these locations during completion of the well before production begins. The tracer at each location is either attached to a section of pipe before it is placed at that location or is delivered into the location while perforating casing at that location. When production begins, monitoring the proportions of the individual tracers in the oil or gas produced by the well allows calculation of the proportions of oil or gas being produced from different zones of the reservoir.

[0007] Tracers have been used in connection with hydraulic fracturing, mainly to provide information on the location and orientation of the fracture. Tracers can also be used for estimating residual oil saturation. Tracers have been used in single well tests and in interwell tests. In single well tests, a tracer is injected into the formation from a well and then produced out of the same well mixed with fluids from the well. The delay in time needed to return to the surface between a tracer that does not react with the formation (a conservative tracer) and one that does (a partitioning tracer) will give an indication of residual oil saturation, a piece of information that is difficult to acquire by other means. In interwell tests, the tracer is injected at one well along with a carrier fluid, such as water in a waterflood, and detected at a producing well after some period of time, which can range from days to years.

[0008] Radioactive and chemical tracers have been used extensively in the oil industry and hydrology testing for decades. Non-radioactive chemical tracers offer distinct advantages over the use of radioactive tracers. For example, there are more unique chemical tracers than radioactive tracers and no downhole logging tools are required.

[0009] Oilfield chemical tracers can be formulated with adjuvant or carrier chemicals before being introduced into a reservoir. When the formulated material is a liquid, the liquid can be pumped down a wellbore to the reservoir. When the formulated material is a solid, it can be pre-placed onto equipment, such as the well bore, before the equipment is placed in the well. Oilfield chemical tracers may be absorbed into the pores of porous carrier particles or encapsulated in a structure in which the oilfield chemical tracer is enclosed, e.g., within a shell of carrier material around the oilfield chemical tracer. Such particles containing oilfield chemicals can then be suspended in a fluid and pumped downhole into the reservoir.

[0010] Despite the wide usage of oilfield chemical tracers, many of the current methods of introducing and using these chemicals have disadvantages.

[0011] One issue is the difficulty in handling oilfield chemical tracers that are in different physical states. For example, when different tracers are placed at their respective locations along the length of a well penetrating a reservoir, a stable solid form of a tracer formulation is normally used. Compared to solid tracers, tracers in liquid and gas form are often difficult to formulate and shape into stable solid objects. This can limit the types of tracers that can be used.

[0012] A further issue is that unwanted inhomogeneous (i.e. non-homogeneous or heterogenous) compositions can result from formulating some oilfield chemical tracers. This is found when attempting to formulate tracers with polymers to form objects for application to hydrocarbon reservoirs resulting in compositions comprising a tracer and polymer having significant non-homogeneous structure and morphology. Such non-homogeneous objects tend to show undesired release behaviour in a subterranean reservoir environment.

[0013] One of the most important issues is the release of oilfield chemical tracers from formulated articles to the targeted fluid or reservoir areas. While it is often a requirement for oilfield chemical tracers to be released in a sustained manner, e.g., slowly so that treatment can be effective over long periods of time (e.g., years), the release of the chemicals in current commercial practice is often too fast (less than 6 months) and not up to the needs of the industry. As a result, some oil field chemical tracers have to be repeatedly introduced into wells to ensure that the requisite level is continuously present in the well. The release of oil field chemical tracers is often not controlled in current practice, causing significant variations over time for both a single tracer and between different tracers. Such issues often result in ineffective monitoring of the reservoir resulting in lost production revenue.

[0014] There are numerous publications describing chemical tracer-based reservoir monitoring. For example, W02001081914 discloses a method of monitoring hydrocarbon and water production from different production zones / sections. Tracer chemicals are covalently linked or linked by ionic interactions to polymers, and the tracers can also be contained in a polymer matrix. The tracers are thus immobilized by means of at least one polymer capable of adhering to the formation, the tracers being covalently bonded or bonded by ionic interactions to the polymer.

[0015] More recently, an improved oilfield chemical release technology has been described by the present applicant in WO2016174413 and WO2021219973. These documents describe oilfield chemical release systems for reservoir treatment or monitoring comprising: (a) microcapsules comprising an oil field chemical and a microencapsulant, wherein the oil field chemical is contained within the microcapsules; and (b) a bulk polymer, where the microcapsules are embedded within the bulk polymer. The use of microcapsules of oilfield chemicals within a bulk polymer matrix has been found to provide two main advantages: (i) microencapsulation enables a controlled and uniform physical and chemical interface to be provided for a range of different oil field chemicals; and (ii) it has been found that microencapsulating the oil field chemicals and then incorporating the microencapsulated oil field chemicals into a bulk polymer matrix enables a more controlled release of the oil field chemicals compared to a configuration in which the oil field chemicals are incorporated directly into a bulk polymer matrix.

[0016] A disadvantage of the microcapsules approach is that there are more manufacturing steps required to microencapsulate the oilfield chemical tracers and then incorporate the microencapsulated tracer into a bulk polymer matrix.

[0017] Another approach, described in WO2016174415, is to incorporate oilfield chemical tracer into a bulk polymer matrix and then coat the bulk polymer matrix to reduce the release rate of the tracer from the bulk polymer matrix and thus increase the time over which tracer is released. Again, a disadvantage of this approach is that there are more manufacturing steps required to incorporate the tracer into a bulk polymer matrix and then coat the bulk polymer matrix.

[0018] Yet another approach for deploying frack tracer is to prepare a solution of a tracer and then absorb as much as possible of the solution onto zeolite particles. The zeolite particles are mixed with the proppant and frack fluids and then used in the fracking operation. The tracer laden zeolite particles become lodged in the rock fractures along with the proppant and the tracer releases from them. However, the tracer release from zeolite particles is rapid and typically can only be detected for a limited time period.

[0019] There is an ongoing need to provide improved oilfield chemical tracer release systems which provide a controlled release of oilfield chemical tracer at desired concentrations, locations, time periods, release rates, and in varying environments to monitor reservoir systems over extended time periods.

[0020] Summary of the Invention

[0021] The present specification is concerned with providing a simple method of immobilizing oilfield chemical tracers, such as oil tracers, in polymer so as to ensure a slow, uniform, and long-time-scale release profile without the requirement for additional components such as microcapsules and / or coatings.

[0022] According to a first aspect, there is provided an oilfield tracer material comprising: a polymer matrix; and an oilfield chemical tracer, wherein the oilfield chemical tracer is an oil tracer, wherein the oilfield tracer material comprises between 5% and 25% by weight of the oil tracer, and wherein the oil tracer is substantially homogeneously dispersed throughout the polymer matrix at a molecular level.

[0023] Intuitively, in order to increase the time period over which a tracer is released from a host polymer matrix, it may be expected that it would be preferable to increase the loading of tracer in the host polymer matrix. Prior art loadings of oil tracer in polymer of 45 wt% have been reported (the percentage of tracer being expressed as the weight of tracer relative to the total weight of tracer and polymer). However, the present inventors have found that this amount of tracer is vastly in excess of what is soluble in the unpolymerized polymer resin. In the prior art, the purpose of the polymer is to immobilize the tracer allowing its release to be slowed. However, the prior art overlooks the fact that while some of the tracer may be dissolved in the polymer, the rest will simply be acting as ‘filler’. The tracer in the polymer acting as ‘filler’ will not be dissolved in the polymer but rather will be present as undissolved tracer. As the unpolymerized polymer resin dissolves some tracer and the rest acts as filler, in use there is a sharp initial release of ‘filler’ tracer followed by a more sustained release from the tracer dissolved in the polymer. However, as there is less polymer to encapsulate the remaining dissolved polymer after the filler has rapidly been released, the sustained release profile is shorter than optimal. As such, over-loading tracer in polymer has been found to be disadvantageous both in terms of the uniformity of tracer release and the longevity of the tracer release. Furthermore, a significant portion of the tracer which acts as filler is effectively wasted.

[0024] It has been found that an oil tracer loading generally in an amount between 5% and 25% can be dissolved in the polymer matrix such that the oil tracer is substantially homogeneously dispersed throughout the polymer matrix at a molecular level. This surprisingly results in an optimum release profile, both in terms of uniformity of tracer release and the longevity of the tracer release. As would be understood by those skilled in the art, mixtures that are homogenously or uniformly mixed on an atomic or molecular level are obtained when a solute dissolves in a solvent. This type of mixing is homogeneous because no boundary is visible in the entire solution. In this way, a homogeneous mixture has a uniform ratio of its components throughout the mixture. Further, this uniformity can be maintained upon solidification of a homogenously mixed solution. Accordingly, in the context of the present invention, the oil tracer being substantially homogeneously dispersed throughout the polymer matrix at a molecular level means the oilfield tracer material has a substantially uniform ratio of the oil tracer and polymer matrix throughout the entirety of the material.

[0025] Optionally, the oilfield tracer material may comprise at least 6%, 7%, or 8% of the oil tracer by weight; no more than 20%, 15%, or 12% of the oil tracer by weight; or an amount of the oil tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

[0026] The polymer matrix may be an epoxy resin, a polyester, or a polyurethane. For example, the polymer matrix may be an epoxy resin comprising an epoxy component and a hardener component.

[0027] Additionally, or alternatively, the polymer matrix may further comprise one or more chain ending or chain branching components. The oil tracer may be a material which is solid at room temperature. The oil tracer may optionally be a halogenated hydrocarbon.

[0028] According to a second aspect, there is provided a polymer bar formed of the oilfield tracer material according to the first aspect.

[0029] Optionally, the polymer bar consists of the oilfield tracer material and is uncoated.

[0030] According to a third aspect, there is provided a plurality of polymer beads formed of the oilfield tracer material according to the first aspect. Optionally, the polymer beads consist of the oilfield tracer material and are uncoated.

[0031] According to a fourth aspect, there is provided a method of manufacturing an oilfield tracer material. The method comprises mixing an oilfield chemical tracer with a polymer forming component, wherein the oilfield chemical tracer is an oil tracer and present in an amount between 5% and 25% by weight; heating the oilfield chemical tracer and the polymer forming component during mixing; and polymerizing the polymer forming component to yield the oilfield tracer material.

[0032] In light of the above, the present specification provides an improved method of manufacturing an oilfield tracer material, the method comprising mixing an oilfield chemical tracer with a polymer forming component and controlling heating of the oilfield chemical tracer and the polymer forming component during mixing. An important feature of the method is that the oilfield chemical tracer is provided in an amount which is sufficiently low that it may be substantially or fully dissolved in the polymer forming component during mixing without any (or at least substantially any) of the oilfield chemical tracer remaining undissolved. That is, the oil tracer and the polymer forming component may form a single phase or substantially form a single phase during heating and mixing.

[0033] Optionally, the heating may be controlled within a temperature range such that: (i) the oilfield chemical tracer fully dissolves in the polymer forming component without any of the oilfield chemical tracer remaining undissolved; (ii) crystallization of the tracer from the polymer forming component is prevented or any crystallized oil tracer is re-dissolved; and (iii) the polymer forming component can be mixed in fluid form to yield a final polymer composition, which is then allowed to polymerize and solidify to yield the oilfield tracer material.

[0034] The method results in an oilfield tracer material in which the oilfield chemical tracer, in the form of an oil tracer, is at least substantially homogeneously dispersed throughout the polymer matrix at a molecular level. As explained above, this has surprisingly been found to result in a long and more uniform tracer release profile.

[0035] As would be understood by those skilled in the art, the property of solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Once dissolved, the solute is uniformly distributed within the solvent. The solubility of a molecule in a liquid medium is an inherent property of the medium and of the molecule (i.e. the solute) at a defined temperature. A homogeneous dispersion may be achieved by ensuring that the solubility limit of the molecule in the liquid medium at a specific temperature is not exceeded. This can be achieved through careful selection and control of a combination of manufacturing parameters: (i) the type of tracer selected; (ii) the type of polymer selected; (iii) the relative solubility of the tracer in the polymer forming component; (iv) the amount of tracer which is mixed with polymer forming component; and (v) the temperature at which the tracer and polymer forming component are blended, taking into account the solubility of the tracer in the polymer forming component and the processability of the polymer forming component at different temperatures. For a given tracer and polymer, testing of different tracer quantities and processing temperatures can be done to select the optimum combination of tracer quantity and processing temperature to ensure that the tracer is fully solubilized in the polymer while ensuring that sufficient tracer is provided for long time scale oilfield tracer applications. It has been found that optimized oilfield tracer materials will typically comprise between 5% and 25% by weight of the oilfield chemical tracer and processing temperatures will typically lie in a range 20°C to 80°C for the step of dissolving the tracer in the polymer forming component, although it will be appreciated that the optimal tracer quantity and processing temperature will vary for different tracer-polymer combinations depending on the relative solubility of the tracer in the polymer forming component. For example, the oilfield tracer material may comprise at least 6%, 7%, or 8% of the oil tracer by weight; no more than 20%, 15%, or 12% of the oil tracer by weight; or an amount of the oil tracer which is in a range defined by any combination of the aforementioned lower and upper limits. Furthermore, the temperature during mixing and heating of the oilfield chemical tracer and the polymer forming component is controlled to be: at least 20°C, 25°C, 30°C, or 40°C; no more than 80°C, 70°C, or 60°C; or within a range defined by any combination of the aforementioned lower and upper limits. Heating may be generated by the process of mixing itself and / or using a heater. Samples of the resulting oilfield tracer material can be analysed under a microscope to confirm that no crystals of tracer are present in the material and that the tracer has dissolved so as to be homogeneously dispersed throughout the polymer matrix at a molecular level. Once the dispersion is homogeneous the medium can be permitted to polymerize. Once polymerized, the homogeneous nature of the molecule dissolved in the liquid medium is maintained even when the temperature falls to ambient as the medium is then solid and no longer permits crystallisation of any dissolved molecule.

[0036] Optionally, after mixing and heating the oilfield chemical tracer in the polymer forming component, a hardener component is added to the mixture, and optionally one or more chain ending or chain branching components, heating being maintained sufficiently such that the polymer forming component can be mixed with the hardener component in fluid form prior to allowing the final composition to polymerize and / or solidify to yield the oilfield tracer material.

[0037] As would be understood by those skilled in the art, a polymer forming component can be any component that can form a suitable polymer matrix. For example, the polymer forming component may be an epoxy, a polyester, or a polyol which generates a polyurethane in the oilfield tracer material.

[0038] According to a fifth aspect, there is provided an oilfield tracer material obtained according to the process of the fourth aspect.

[0039] According to a sixth aspect, there is provided a method of oilfield tracing. The method comprises: introducing an oil field tracer material according to the first or fifth aspects, a polymer bar according to second aspect, or a plurality of polymer beads according to the third aspect into a hydrocarbon reservoir, well, or wellbore; and monitoring for release of oil field chemical tracer from the oil field tracer material.

[0040] Optionally, the oilfield tracer material may be in the form of polymer beads which are injected into the hydrocarbon reservoir, well, or wellbore with proppant and frack fluid.

[0041] Brief Description of the Drawings

[0042] For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0043] Figure 1 shows elution test data for Example 1 , which is a polymer bar of the present invention, and Comparative Examples 1 and 2;

[0044] Figure 2 shows elution test data for three polymer bar formulations which have varying amounts of monofunctional chain termination within the polymer;

[0045] Figure 3 which shows elution test data for two polymer bar formulations which have varying amounts of cross-linking additive;

[0046] Figure 4 shows elution test data for three formulations eluted at 85, 90 & 95°C to illustrate the effects of temperature changes on tracer release rate;

[0047] Figure 5 shows elution test data for samples with different post curing treatments; and

[0048] Figure 6 shows elution test data for samples with different polymer bead sizes.

[0049] Detailed Description

[0050] The present specification provides an oilfield tracer material comprising: a polymer matrix; and an oilfield chemical tracer, wherein the oilfield chemical tracer is an oil tracer, wherein the oilfield tracer material comprises between 5% and 25% by weight of the oil tracer, and wherein the oil tracer is homogeneously dispersed throughout the polymer matrix at a molecular level. The oil tracer may be substantially solubilized / miscible in the polymer forming component during manufacture (i.e. less than 10%, preferably less than 5% remains undissolved in the polymer forming component) so as to ensure slower and more uniform release in use with the tracer being immobilized far more securely with the associated polymer. In some examples, the oil tracer is essentially completely dissolved during manufacture (i.e., less than 2% remains undissolved in the polymer forming component). In some examples, the oil tracer may be completely solubilized / miscible in the polymer forming component during manufacture. The present methodology is particularly suited to ensure that oil tracers which are solid at room temperature are fully dissolved in a host polymer matrix without substantial levels of undissolved solid filler or crystallized oil tracer material in the host polymer matrix. As such, the present oilfield tracer material may comprise an oil tracer which is conventionally solid, e.g., a solid crystalline material, at room temperature but which is molecularly dispersed in the polymer matrix by the manufacturing method such that no solid crystals of oil tracer material are present within the polymer matrix when viewed under a microscope. In the event that the oil tracer is a liquid rather than a solid at room temperature, it has been found that providing the same relative quantities of liquid oil tracer and polymer matrix can also ensure that a liquid oil tracer is fully miscible in the polymer matrix such that the oil tracer is homogeneously dispersed throughout the polymer matrix at a molecular level. As such, the terms “substantially homogenously dispersed”, “homogenously dispersed”, “substantially or fully dissolved” or “substantially or fully solubilized” also cover oil tracer materials which may be liquid at room temperature unless stated otherwise.

[0051] The oilfield tracer material may comprise at least 5%, 6%, 7%, or 8% of the oilfield chemical tracer by weight; no more than 25%, 20%, 15%, or 12% of the oilfield chemical tracer by weight; or an amount of the oilfield chemical tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

[0052] The oilfield chemical tracer is an oil tracer. An oil tracer is a chemical which can be added to a flow of oil from a reservoir for the purposes of identifying a specific flow of oil and distinguishing the flow of oil from any other flow of oil. The oil tracer is preferably soluble in the oil. The oil tracer is preferably a molecule which is not known to occur naturally in the oil.

[0053] In this case, the polymer matrix may be an epoxy resin, a polyester, or a polyurethane formed from a polyol. For example, the polymer matrix may be an epoxy resin comprising an epoxy component, a hardener component, and optionally one or more chain ending or chain branching components. Chain ending additives can be included to reduce polymer cross-linking and increase tracer release rate. Conversely, chain branching components can be included to increase polymer cross-linking and decrease tracer release rate. Such additives can thus be used to tune the release rate of a tracer to a desired level for a particular application. In accordance with the present specification, by ensuring that the tracer material is substantially or fully dissolved in the polymer material, such tuning can be better optimized as the rapid release of undissolved tracer material is avoided and the cross-linking of the polymer matrix is more effective in controlling the release of the fully dissolved tracer material. As such, tracer release of materials according to the present specification is more controllable.

[0054] A polymer bar can be formed of the oilfield tracer material as described herein. The polymer bar may comprise or consist essentially of the oilfield tracer material. Alternatively, the polymer bar may consist only of the oilfield tracer material and be uncoated. Using the oilfield tracer material as described herein can achieve slow and uniform release of the tracer without the need for a coating as described in the prior art. The polymer bar can be used in down-hole tracing methods. Additionally, or alternatively, a plurality of polymer beads can be formed of the oilfield tracer material as described herein. Again, the plurality of polymer beads may comprise or consist essentially of the oilfield tracer material, or consist of only the oilfield tracer material and be uncoated. The polymer beads can be formed directly during material manufacture, or a polymer bar can be formed as described above and then processed into a plurality of polymer beads.

[0055] The amount of tracer and the amount of polymer forming coating can be selected such that the resultant oilfield tracer material comprises: at least 5%, 6%, 7%, or 8% of the oilfield chemical tracer by weight; no more than 25%, 20%, 15%, or 12% of the oilfield chemical tracer by weight; or an amount of the oilfield chemical tracer which is in a range defined by any combination of the aforementioned lower and upper limits. Alternatively, or additionally, the quantity of oil tracer material can be expressed relative to the amount of polymer forming component in the mixing and heating step prior to adding any other components such as hardener. In this case, similar numbers apply and the mixture of oilfield chemical tracer and polymer forming component may comprise: at least 5%, 6%, 7%, or 8% of the oilfield chemical tracer by weight; no more than 25%, 20%, 15%, or 12% of the oilfield chemical tracer by weight; or an amount of the oilfield chemical tracer which is in a range defined by any combination of the aforementioned lower and upper limits. Quantities are selected such that the oil tracer substantially or fully dissolves in the polymer forming component during mixing and heating. For example, less than 10%, preferably less than 5% remains undissolved in the polymer forming component. In some examples, the oil tracer is essentially completely dissolved during manufacture (i.e., less than 2% remains undissolved in the polymer forming component). In some examples, the oil tracer may be completely solubilized in the polymer forming component. An example tracer concentration in the polymer is about 10% w / w. However, the actual amount of tracer which will dissolve in the unpolymerized polymer will depend upon the actual tracer chemical and also the processing temperature. In this regard, the temperature during mixing and heating of the oilfield chemical tracer and the polymer forming component can be controlled to be: at least 20°C, 25°C, 30°C, or 40°C; no more than 80°C, 70°C, or 60°C; or within a range defined by any combination of the aforementioned lower and upper limits. The heating can be generated by the process of mixing and / or using a heater. The temperature should be sufficient to ensure that the oil tracer dissolved in the polymer forming component while being controlled such that it does not cause any unwanted reactions or crystallizations.

[0056] After substantially or fully dissolving the oilfield chemical tracer in the polymer forming component, the polymer forming component can be mixed with a hardener component, and optionally one or more chain ending or chain branching components, heating being maintained sufficiently such that the polymer forming component can be mixed with the hardener component in fluid form prior to allowing the final composition to polymerize and / or solidify to yield the oilfield tracer material.

[0057] The present specification also provides a method of oilfield tracing, the method comprising: introducing an oilfield tracer material, a polymer bar, or a plurality of polymer beads as described herein into a hydrocarbon reservoir, well, or wellbore; and monitoring for release of oil field chemical tracer from the oil field tracer material. According to certain examples, the oilfield tracer material is in the form of polymer beads which are injected into the hydrocarbon reservoir, well, or wellbore with proppant and frack fluid. Examples include the incorporation of oil soluble tracer chemicals into polymer beads. The polymer can be epoxy resin. A typical procedure for making an epoxy resin is to blend the epoxy containing component with a hardener component, optionally with chain ending or chain branching components. The tracer chemical is dissolved in the epoxy containing component such that the concentration of dissolved oil tracer is as great as possible but additionally so that none or substantially none of the oil tracer remains undissolved. The blend of tracer and epoxy component should be heated to ensure dissolution of the tracer. The temperature should be suitably controlled to prevent crystallization of the tracer from the epoxy component but maintained sufficiently such that the epoxy containing component can then be mixed with hardener component and any other additives and polymerization left to occur.

[0058] The result of dissolving the tracer in the epoxy component is that the tracer is homogeneously dispersed throughout the epoxy component. When the components of the epoxy resin have polymerized the tracer is still held in a uniform distribution throughout the epoxy matrix (without being chemically bound to the epoxy component). The proportion of the tracer is constant throughout the resin. The benefit of this approach is that the tracer is immobilized far more securely with the associated polymer particles, and after being deployed with a proppant and frack fluids is still detectable after 200 days. The other benefit over zeolite particles containing tracer is that the proportion of tracer held in the polymer beads greatly exceeds the proportion of tracer which can be adsorbed onto zeolite particles.

[0059] A homogenous solution of tracer in a polymer can be cast as a bar and then chipped into beads. This approach provides a means of deploying frack tracers from a concentrated but homogeneous matrix. Alternatively, the tracer-polymer forming solution can be printed or formed as discrete particles. This removes the need to cast a bar followed by chipping the bar.

[0060] Dissolving tracers in a polymer bar presents a simpler way of generating slow- release tracer formulations compared with using micro-encapsulation and is not as wasteful in terms of tracer loading as a 45% (undissolved) dispersion of tracer in a polymer bar. The use of homogeneous tracer solutions in a polymer means that the release rate is more uniform when they are produced as polymer beads. The current alternative process is to use micro-encapsulated tracer in bars which are then chipped. The chipping process can result in the advantage of microencapsulating the solid tracer being reduced or lost.

[0061] Example of oil tracer polymer bead manufacturing method

[0062] The following example details the formulation and method used to manufacture oil tracer polymer bars (primary products) which are milled to make oil tracer polymer beads (secondary product).

[0063] Raw Materials

[0064] • AH110 Epoxy resin (available from Ebalta)

[0065] • TGS Epoxy resin hardener (available from Ebalta)

[0066] • T-7XX - Tracerco oil tracers

[0067] • Silicone release agent

[0068] • Acetone

[0069] Apparatus

[0070] • Balance (1 decimal place)

[0071] • Polypropylene buckets (2.5 L - 10 L)

[0072] • Silverson® Mixer

[0073] • Spatula

[0074] • Helix mixer / drill

[0075] • Silicone moulds (coated with silicone release agent)

[0076] • Oven (Heating I Curing Polymer)

[0077] Mill Oil Tracer Recipe

[0078] The table below shows the mixing ratio which should be followed for a standard oil tracer bar (primary product):

[0079] The table below shows an example of mixing weight for a 1 kg batch size: The table below show an example of mixing weight for a 10 kg batch size:

[0080] Formulation, casting, and curing process 1. Prior to formulating, sieve the oil tracer through an 850-micron sieve (break up any larger lumps with a pestle and mortar). 2. Pre-weigh a suitable mixing containing (e.g., 12.5 L container for 10 kg batch size) on a balance and add the required amount of AH110 epoxy resin (e.g., 7.5 kg)

[0081] 3. Weigh the required amount of selected oil tracer into a suitable container (e.g., 1.0 kg).

[0082] 4. Immerse the head of a Silverson® mixer in the AH110 epoxy resin and begin to mix.

[0083] 5. Increase the speed of the Silverson® mixer gradually until the AH110 epoxy resin is warm (<50°C) and a speed of at least 3000 rpm can be maintained.

[0084] 6. Add oil tracer gradually, ensuring continuously mixing and maintain the temperature at <50°C.

[0085] 7. The Silverson® mixer will reduce the particle size and the tracer will become partially / fully soluble.

[0086] 8. The mixture is deemed to be fully mixed once the resin is homogenous and without any visible solids.

[0087] 9. Scrape down the sides and the bottom of the mixing container with a spatula and mix for a further 2 minutes.

[0088] 10. Once prepared, the mixture must be sealed and stored at 18-25°C. If the temperature drops below 18°C the tracer may recrystalise in the resin. The tracer can be resolubilised into the AH110 resin upon mixing / heating to 50°C.

[0089] 11. Clean the Silverson® mixer with acetone to remove any resin and tracer.

[0090] 12. When ready to cast, weigh aliquots of the polymer / tracer mixture into suitable mixing pots (e.g., 2.5L mixing pot for a 0.85 kg aliquot)

[0091] 13. Add the required amount of TGS added (e.g., 0.15 kg).

[0092] 14. Stir the mixture with a helix drill mixer until fully mixed.

[0093] 15. Spray the silicone mould with silicone release agent and place it on a removable oven wire shelf.

[0094] 16. Carefully pour the mixture (e.g., 1 kg) into a level silicone mould ensuring not to overfill.

[0095] 17. Transfer the filled mould and wire shelf into the oven and cure at 60°C for 1 hour until the products have cured.

[0096] 18. Once cured, transfer the mould(s) to a flat surface to cool.

[0097] 19. The bar products can be demoulded once cooled.

[0098] 20. Finished primary products should be packaged into seal polythene bags and labelled with a. Oil tracer T-number and percentage. b. Date of manufacture. c. Manufacturer.

[0099] 21. Finished primary oil tracer bar products (7 x 7 x 350 mm) can be milled inhouse or sent to a third party for milling.

[0100] Milling and sieving

[0101] Finished primary oil tracer bar products (7 x 7 x 400 mm) can be milled on any milling machine to give polymer beads of the correct size of 40 / 70 mesh (425-212 micron).

[0102] The secondary polymer bead product should be separated using a stacked sieve system to separate polymer beads into fractions of

[0103] • 20 / 40 Mesh = Beads too large - can be re-milled to reduce particle size.

[0104] • 40 / 70 Mesh = Desired Product.

[0105] • 70 / 100 Mesh and below = Beads / powder kept for rework.

[0106] The table below show Mesh size conversion to micron and millimeters.

[0107] Examples of the effect of tracer release

[0108] The elution profile was tested for the following three polymer bar formulations:

[0109] Example 1 - A tracer bar comprising 10 wt.% of an oil tracer (T-729, available from Tracerco) in AH110:TGS (100:20), which was prepared in accordance with the “Formulation, casting, and curing process” described above. Comparative Example 1 - A tracer bar comprising 10 wt.% of an oil tracer (T-729, available from Tracerco) in AH110:TGS (100:20) and prepared in the same manner as Example 1 with the exception that the components were mixed on a Dispermat® mixer, which mixes without generating heat. That is, no heat was generated or externally applied during mixing of the oil tracer with the polymer forming component in Comparative Example 1.

[0110] Comparative Example 2 - A tracer bar comprising 45 wt.% of an oil tracer (T-729, available from Tracerco) in AH110:TGS (100:20) and prepared in the same manner as Comparative Example 1.

[0111] The elution profiles at 90°C of the tracer bars (i.e. without milling) described above are shown in Figure 1. As shown in Figure 1, Example 1 exhibited significantly reduced elution rates under the elution testing compared to Comparative Examples 1 and 2. In particular, the percentage tracer released after a period of seven days for Example 1 was 0.05%, which compared to 22.6 % for Comparative Example 1 and 20.6 % for Comparative Example 2. Indeed, Example 1 showed a slow and uniform release profile over the whole testing period, demonstrating a clear capacity for longer time scale release of the tracer from the polymer matrix without the requirement for use of microencapsulation and / or coatings.

[0112] Examples of oilfield tracer material formulations

[0113] The following examples show how formulations comprising a polymer forming component (AH110 Epoxy resin available from Ebalta), a hardener (TGS Epoxy resin hardener available from Ebalta), and a tracer (oilfield tracers available from Tracerco) can be modified with additives to improve and / or tune tracer release performance. The examples show the effects on tracer release as shown via elution tests due to:

[0114] • formulation component mixing ratios

[0115] • additives

[0116] • curing temperature

[0117] • additional curing time

[0118] • particle size The examples show formulations used in the manufacture of inflow tracer bars and subsequent polymer bead products and the effects additives, method of manufacture, and curing temperatures have on tracer release rates when added to a standard epoxy resin polymer formulation.

[0119] Standard Epoxy Resin Formulation

[0120] A standard epoxy resin formulation consists of two components: an epoxy resin polymer forming component (e.g., AH110 Epoxy resin available from Ebalta) and a hardener (e.g., TGS Epoxy resin hardener available from Ebalta). Details of these components can be found in the following documents: Ebalta AH110 Safety Data Sheet (SDS) [Version 6. Revision 26.08.2011]; Ebalta TGS Safety Data Sheet SDS (SDS) [Version 6. Revision 29.04.2015.]; and AH110 / TGS Technical Data Sheet TDS [22.01.2008. Revision 1]):

[0121] Component 1: AH110 epoxy resin - a reaction product of bisphenol-A- (epichlorhydrin) epoxy resin (number average molecular weight = 700), bisphenol-F- epichlorhydrine resin MG <700, and 1,6-hexandioldiglycidylether; and

[0122] Component 2: TGS amine hardener - a reaction product of 3,6- diazaoctanethyleenediamin and benzyl alcohol.

[0123] The supplier recommended mixing ratio of AH110:TGS is 100:22 parts by weight (pbw). However, for oilfield tracer material formulations the present applicant has found it useful to utilize a slightly modified mixing ratio of 100:20 or 5:1 parts by weight (pbw). That said, this ratio may be altered to increase or decrease the level of tracer release required for a given temperature in use.

[0124] The supplier recommended curing time and temperature is 6 to 8 hours at room temperature, with a post cure for 12 hours at 80°C. However, for oilfield tracer material formulations, the present applicant has found it useful to utilize a curing time and temperature of 1 hour at 60°C, with an option for a post cure for 4 hours at 80°C if required. The present applicant has added halogenated hydrocarbon tracers into the above polymer formulations at < 50% wt / wt to produce solid articles for reservoir studies. No reaction occurs between the polymer and the tracer. The polymer provides a structure from which the tracer migrates / releases into surrounding fluid in use.

[0125] Manufacturing Method

[0126] AH110 epoxy resin is added by weight into a container. If an additive is included, for example Epodil® 748 or DEN 438 (additives described later), it is added at this stage replacing a percentage of the AH110 weight. At this stage, the resin can be mixed on a Dispermat® mixer which mixes without generating heat.

[0127] The required weight of tracer is then added. Where solid tracer polymer bar articles are required for polymer bead applications, tracer is included in the AH110 epoxy resin at levels of approximately 10%. An additional mixing step takes place, using a wet milling Silverson® mixer, which reduces the tracer particle size and generates heat in the resin blend. In this regard, it is to be noted that heating is not required to blend AH110 and Epodil® 748. However, in accordance with the present specification, heat is required to enable the tracer to dissolve. Furthermore, heat is required to blend AH110 and DEN 438, due to the high viscosity nature of the DEN 438. Again, heat is also required to enable the tracer to dissolve. The heating to dissolve the tracer during mixing can be provided by heating or pre-heating of components or through mixing using a mixer which itself generates heat by the mixing process, e.g., a Silverson® mixer. Care must be taken to ensure that the mixture is not over heated, e.g., keeping the temperature below 80°C, preferably below 60°C.

[0128] A portion of the tracer / resin blend is transferred into a second container and, using the correct mixing ratio, the TGS amine hardener is calculated and weighed into the second container and blended at room temperature. The resultant liquid polymer blend is cast into silicone moulds, which had been previously sprayed with release agent, and placed into an oven to cure for 1 hour at 60°C. After 1 hour the moulds are removed from the oven and left to cool at room temperature, before the solid tracer polymer bar articles are demoulded ready for use.

[0129] At 10% loading, halogenated hydrocarbon tracers used as oil tracers fully dissolve into solution, becoming soluble in the epoxy resin and once reacted with the TGS hardener, show a longer period of release when compared to a standard saturated filled tracer formulation.

[0130] Addition of Epodil® 748 additive to Standard Epoxy Resin Formulation

[0131] Epodil® 748 is an aliphatic glycidyl ether. It is a monofunctional reactive diluent used to reduce the viscosity of epoxy resin systems. The literature indicates that since monofunctional diluents cause molecular weight chain termination, the minimum amount necessary to achieve the desired viscosity reduction should be used (see Epodil®748 Reactive Diluent Technical Data Sheet TDS, and https: / / crosslinkersweb.panpage.de / en2 / crosslinkers / epodil / usa / epodil_748_us.pdf). The present applicant has found that adding Epodil®748 into a standard AH 110: TGS epoxy formulation, replacing a portion of the AH110 epoxy resin, reduces crosslinking via monofunctional chain termination within the polymer and increases tracer release into an aqueous or hydrocarbon media. As such, chain terminating additives can be used to tune tracer release.

[0132] Examples of the effect of tracer release with Epodil® 748 added to the standard epoxy resin formulation are illustrated in Figure 2 which shows elution test data (90°C elution testing) for the following three polymer bar formulations which have varying amounts of Epodil® 748 (E748) additive:

[0133] *pbw = parts by weight Figure 2 shows that when parts of the AH110 epoxy resin component are replaced by Epodil® 748 additive, the percentage of tracer release increases. That is, addition of a chain termination or chain ending additive reduces cross-linking of the polymer matrix and increases the rate of oil tracer release in use.

[0134] It should be noted that in relation to the material samples in the above table and Figure 2, the tracer quantities were too high, and the materials included some undissolved tracer. According to the present specification, the tracer quantity should be reduced to avoid undissolved tracer. However, these examples are included to show the effect of using chain ending additives to tune tracer release. Such additives can also be used to tune the release rate of oilfield tracer materials of the present specification while advantageously and simultaneously avoiding an initial rapid release of tracer due to crystallized tracer in the host polymer matrix. As such, the combination of fully dissolved tracer with additives which tune cross-linking of the polymer matrix is advantageous as the tuning of the cross-linking is more effective at controlling release of dissolved tracer versus undissolved tracer.

[0135] Addition of DEN 438 additive to Standard Epoxy Resin Formulation

[0136] According to the literature DEN 438 epoxy novolac resin is a semi-solid reaction product of epichlorohydrin and phenol-formaldehyde novolac. It has multi-epoxy functionality. These additional reactive sites produce tightly cross-linked cured systems. This makes DEN 438 epoxy novolac resin useful in adhesives, structural laminates, coatings and castings for elevated temperature service (see Form No. 296-01443-1001XSI.pdf from Dow Plastics).

[0137] The present applicant has found that adding DEN 438 into a standard AH 110: TGS epoxy formulation, replacing a portion of the AH110 epoxy resin, increases crosslinking within the polymer and slows tracer release into an aqueous or hydrocarbon media. As such, cross-linking additives can be used to tune tracer release.

[0138] Examples of the effect of tracer release with DEN 438 added to the standard epoxy resin formulation are illustrated in Figure 3 which shows elution test data (120°C elution testing) for the following two polymer bar formulations which have varying amounts of DEN 438 additive:

[0139] In relation to the above table and Figure 3, it should be noted that percentage of DEN = percentage of DEN 438 which replaces the AH110 and not the percentage of DEN 438 in the overall formulation. For example, the standard formulation contains AH110 (50pbw). Therefore, a formulation containing AH110 (37.5pbw) + DEN438 (12.5pbw) = Total (50pbw). Therefore, 12.5pbw 150 pbw x 100 = 25% DEN 438.

[0140] Figure 3 shows that when parts of AH110 epoxy resin component are replaced by DEN 438 the percentage of tracer release decreases. That is, addition of a crosslinking additive increases cross-linking of the polymer matrix and decreases the rate of oil tracer release in use. Again, it should be noted that in relation to the material samples in the above table and Figure 3, the tracer quantities were too high, and the materials included some undissolved tracer. According to the present specification, the tracer quantity should be reduced to avoid undissolved tracer. However, these examples are included to show the effect of using cross-linking additives to tune tracer release. Such additives can also be used to tune the release rate of oilfield tracer materials of the present specification while advantageously and simultaneously avoiding an initial rapid release of tracer due to crystallized tracer in the host polymer matrix. As such, the combination of fully dissolved tracer with additives which tune cross-linking of the polymer matrix is advantageous as the tuning of the cross-linking is more effective at controlling release of dissolved tracer versus undissolved tracer.

[0141] Effect of temperature on tracer release rate in AH110 / TGS based polymer formulations

[0142] Three identical polymer tracer formulations were prepared as follows:

[0143] Figure 4 shows the tracer release profiles for the three formulations eluted at 85, 90 & 95°C to show effects of temperature changes on tracer release rate. Elution rate is highest at 95°C, lowest at 85°C, and intermediate at 90°C. Again, it should be noted that in relation to the material samples in the above table and Figure 4, the tracer quantities were too high, and the materials included some undissolved tracer. According to the present specification, the tracer quantity should be reduced to avoid undissolved tracer. However, these examples are included to show the effect of temperature on tracer release rate. The basic principle of increased temperature resulting in increased release rate also applies to oilfield tracer materials of the present specification while advantageously and simultaneously avoiding an initial rapid release of tracer due to crystallized tracer in the host polymer matrix. Indeed, the tracer release rate is more controllable for a target temperature using the present specification as it avoids uncontrolled release of undissolved tracer material.

[0144] Effect of post cure on tracer release rate in AH110 / TGS based polymer formulations

[0145] Three similar polymer tracer formulations were prepared as follows:

[0146] All three samples were cured at 60°C. The three samples were then subjected to different post curing treatments at 80°C. Sample 120 1 had no 80°C post cure treatment. Sample 120 / 721 / C4 had an 80°C post cure for 4 hours. Sample 120 / 721 / C12 had an 80°C post cure for 12 hours. As shown in Figure 5, the samples which were subjected to the 80°C post cure treatment exhibited significantly reduced elution rates under 120°C elution testing Again, it should be noted that in relation to the material samples in the above table and Figure 5, the tracer quantities were too high, and the materials included some undissolved tracer. According to the present specification, the tracer quantity should be reduced to avoid undissolved tracer. However, these examples are included to show the effect of applying a post curing treatment on tracer release rate. The basic principle of post-cure heat treatments resulting in decreased tracer release rate also applies to oilfield tracer materials of the present specification while advantageously and simultaneously avoiding an initial rapid release of tracer due to crystallized tracer in the host polymer matrix. As such, the combination of fully dissolved tracer with post curing treatment which tunes the polymer matrix is advantageous as the tuning of the polymer matrix is more effective at controlling release of dissolved tracer versus undissolved tracer.

[0147] Effect of polymer bead particle size on release rate in AH110 / TGS based polymer formulations

[0148] Four identical polymer tracer formulations were prepared but then processed to provide four samples having polymer beads I particles with differing particle sizes as follows:

[0149] In the above table the samples are ordered in decreasing particle size (20 / 40 Mesh being larger than > 100 Mesh). As shown in Figure 6, as polymer bead size decreases, elusion rate increases. The tracer release rate is more controllable via particle size changes using the present specification as it avoids uncontrolled release of undissolved tracer material. Examples of oil tracers

[0150] Tracers used to track the movement of oil soluble materials generally have low water solubility (e.g. <100mg / L) and high (>1000) organic / water partition coefficients.

[0151] Several families of such compounds have been used. Oil tracers which can be used in the present specification include halogenated hydrocarbons. Examples of oil tracers that can be incorporated into the polymer formulations of the present specification include halogenated anthracenes, halogenated benzenes, and halogenated benzophenones. Hydrocarbons may have one, two, three or four halogen substitutes which may be the same or different and include bromine and / or chlorine substituents. The halogenated hydrocarbons may be solid at room temperature. Examples of such oil tracers include the following:

[0152] Mixtures of these compounds can also be used although single compounds are preferred. Such oil tracers may advantageously be used in combination with epoxy resin polymer systems.

[0153] There is a growing requirement for the long-term assessment of open propped fracture oil and water stage flows with measurement of the cross flow. This requires the use of solid tracers so that the tracer remains where the solid proppants are placed in a well during the fracturing and propping process. The present specification addresses this requirement.

[0154] It has been shown that for a given tracer it is possible to select a polymer system and control the quantity of tracer and the polymer processing conditions (temperature) so that the tracer is substantially or fully dissolved in the polymer forming component and that this results in an oilfield tracer material in which the tracer is substantially or fully homogeneously dispersed throughout the polymer matrix at a molecular level without any significant levels of solid tracer “filler” material. It has further been found that this results in more uniform and longer time scale release of the tracer from the polymer matrix without the requirement for use of microencapsulation and / or coatings.

[0155] In addition to the above, it has been found that the release profile of such an oilfield tracer material can be tuned using additives to increase or decrease the tracer release rate. Chain terminating additives can be used to reduce crosslinking within the polymer and increase tracer release into a hydrocarbon media. Conversely, cross-linking additives can be used to increase crosslinking within the polymer system and slow tracer release into a hydrocarbon media.

[0156] Further tuning can be achieved by post curing the oilfield tracer material to reduce tracer release rates and / or processing the polymer to different polymer bead sizes with smaller polymer beads releasing tracer more rapidly than larger polymer beads.

[0157] It has been found that such additives and processing methods used to tune tracer release from the polymer matrix are more effective when the tracer material is substantially or fully dissolved in the polymer matrix as uncontrolled release of undissolved solid tracer material is avoided. That is, the release profile of the tracer is more intimately related to the polymer matrix structure when it is substantially or fully dissolved in the polymer matrix structure and thus the tracer release profile can be better controlled I tuned through changes to the polymer matrix structure.

[0158] The present disclosure can be further described in a number of aspects, including, but not limited to those described below:

[0159] Clause 1. An oilfield tracer material comprising: a polymer matrix; and an oilfield chemical tracer, wherein the oilfield chemical tracer is an oil tracer, wherein the oilfield tracer material comprises between 5% and 25% by weight of the oil tracer, and wherein the oil tracer is dissolved in the polymer matrix such that the oil tracer is homogeneously dispersed throughout the polymer matrix at a molecular level.

[0160] Clause 2. An oilfield tracer material according to clause 1 , wherein the oilfield tracer material comprises at least 6%, 7%, or 8% of the oil tracer by weight; no more than 20%, 15%, or 12% of the oil tracer by weight; or an amount of the oil tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

[0161] Clause 3. An oilfield tracer material according to clause 1 or 2, wherein the polymer matrix is an epoxy resin, a polyester, or a polyurethane.

[0162] Clause 4. An oilfield tracer material according to any preceding clause, wherein the polymer matrix is an epoxy resin comprising an epoxy component and a hardener component.

[0163] Clause 5. An oilfield tracer material according to any preceding clause, wherein the polymer matrix further comprises one or more chain ending or chain branching components.

[0164] Clause 6. An oilfield tracer material according to any preceding clause, wherein the oil tracer is a material which is solid at room temperature.

[0165] Clause 7. An oilfield tracer material according to any preceding clause, Wherein the oil tracer is a halogenated hydrocarbon.

[0166] Clause 8. A polymer bar formed of the oilfield tracer material according to any preceding clause.

[0167] Clause 9. A polymer bar according to clause 8, wherein the polymer bar consists of the oilfield tracer material and is uncoated. Clause 10. A plurality of polymer beads formed of the oilfield tracer material according to any one of clauses s 1 to 7.

[0168] Clause H . A plurality of polymer beads according to clause 10, wherein the polymer beads consist of the oilfield tracer material and are uncoated.

[0169] Clause 12. A method of manufacturing an oilfield tracer material, the method comprising: mixing an oilfield chemical tracer with a polymer forming component, wherein the oilfield chemical tracer is an oil tracer; heating the oilfield chemical tracer and the polymer forming component during mixing, wherein the oilfield chemical tracer is provided in an amount which is sufficiently low that it fully dissolves in the polymer forming component during mixing and heating without any of the oilfield chemical tracer remaining undissolved, and wherein the heating is controlled within a temperature range such that: the oil tracer fully dissolves in the polymer forming component without any of the oil tracer remaining undissolved; crystallization of the oil tracer from the polymer forming component is prevented or wherein any crystallized oil tracer is re-dissolved; and the polymer forming component can be mixed in fluid form to yield a final polymer composition; and allowing the final polymer composition to polymerize to yield the oilfield tracer material.

[0170] Clause 13. A method according to clause 12, wherein the oilfield tracer material comprises at least 5%, 6%, 7%, or 8% of the oilfield chemical tracer by weight; no more than 25%, 20%, 15%, or 12% of the oilfield chemical tracer by weight; or an amount of the oilfield chemical tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

[0171] Clause 14. A method according to clause 12 or 13, wherein the temperature during mixing and heating of the oilfield chemical tracer and the polymer forming component is controlled to be: at least 20°C, 25°C, 30°C, or 40°C; no more than 80°C, 70°C, or 60°C; or within a range defined by any combination of the aforementioned lower and upper limits.

[0172] Clause 15. A method according to any one of clauses 12 to 14, wherein the heating is generated by the process of mixing and / or using a heater.

[0173] Clause 16. A method according to any one of clauses 12 to 15, wherein after fully dissolving the oilfield chemical tracer in the polymer forming component, the polymer forming component is mixed with a hardener component, and optionally one or more chain ending or chain branching components, heating being maintained sufficiently such that the polymer forming component can be mixed with the hardener component in fluid form prior to allowing the final composition to polymerize and / or solidify to yield the oilfield tracer material.

[0174] Clause 17. A method according to any one of clauses 12 to 16, wherein the polymer forming component is an epoxy, a polyester, a polyol which generates a polyurethane in the oilfield tracer material.

[0175] Clause 18. A method of oilfield tracing, the method comprising: introducing an oil field tracer material according to any one of clauses 1 to 7, a polymer bar according to clauses 8 or 9, or a plurality of polymer beads according to clauses 10 or 11 into a hydrocarbon reservoir, well, or wellbore; and monitoring for release of oil field chemical tracer from the oil field tracer material.

[0176] Clause 19. A method according to clause 18, wherein the oilfield tracer material is in the form of polymer beads which are injected into the hydrocarbon reservoir, well, or wellbore with proppant and frack fluid.

[0177] While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. An oilfield tracer material comprising: a polymer matrix; and an oilfield chemical tracer, wherein the oilfield chemical tracer is an oil tracer, wherein the oilfield tracer material comprises between 5% and 25% by weight of the oil tracer, and wherein the oil tracer is substantially homogeneously dispersed throughout the polymer matrix at a molecular level.

2. An oilfield tracer material according to claim 1, wherein the oilfield tracer material comprises at least 6%, 7%, or 8% of the oil tracer by weight; no more than 20%, 15%, or 12% of the oil tracer by weight; or an amount of the oil tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

3. An oilfield tracer material according to claim 1 or 2, wherein the polymer matrix is an epoxy resin, a polyester, or a polyurethane.

4. An oilfield tracer material according to any preceding claim, wherein the polymer matrix is an epoxy resin comprising an epoxy component and a hardener component.

5. An oilfield tracer material according to any preceding claim, wherein the polymer matrix further comprises one or more chain ending or chain branching components.

6. An oilfield tracer material according to any preceding claim, wherein the oil tracer is a material which is solid at room temperature.

7. An oilfield tracer material according to any preceding claim, wherein the oil tracer is a halogenated hydrocarbon.

8. A polymer bar formed of the oilfield tracer material according to any preceding claim.

9. A polymer bar according to claim 8, wherein the polymer bar consists of the oilfield tracer material and is uncoated.

10. A plurality of polymer beads formed of the oilfield tracer material according to any one of claims 1 to 7.

11. A plurality of polymer beads according to claim 10, wherein the polymer beads consist of the oilfield tracer material and are uncoated.

12. A method of manufacturing an oilfield tracer material, the method comprising: mixing an oilfield chemical tracer with a polymer forming component, wherein the oilfield chemical tracer is an oil tracer and present in an amount between 5% and 25% by weight; heating the oilfield chemical tracer and the polymer forming component during mixing; and polymerizing the polymer forming component to yield the oilfield tracer material.

13. A method according to claim 12, wherein the oilfield chemical tracer is substantially dissolved in the polymer forming component during mixing and heating.

14. A method according to claim 12 or 13, wherein the heating is controlled within a temperature range such that: the oil tracer fully dissolves in the polymer forming component without any of the oil tracer remaining undissolved; crystallization of the oil tracer from the polymer forming component is prevented or wherein any crystallized oil tracer is re-dissolved; and the polymer forming component can be mixed in fluid form to yield a final polymer composition.

15. A method according to claim 12 to 14, wherein the temperature during mixing and heating of the oilfield chemical tracer and the polymer forming component is controlled to be: at least 20°C, 25°C, 30°C, or 40°C; no more than 80°C, 70°C, or 60°C; or within a range defined by any combination of the aforementioned lower and upper limits.

16. A method according to any one of claims 12 to 15, wherein the oilfield tracer material comprises at least 6%, 7%, or 8% of the oilfield chemical tracer by weight; no more than 20%, 15%, or 12% of the oilfield chemical tracer by weight; or an amount of the oilfield chemical tracer which is in a range defined by any combination of the aforementioned lower and upper limits.

17. A method according to any one of claims 12 to 16, wherein the heating is generated by the process of mixing and / or using a heater.

18. A method according to any one of claims 12 to 17, wherein after mixing and heating the oilfield chemical tracer in the polymer forming component, a hardener component is added to the mixture, and optionally one or more chain ending or chain branching components, heating being maintained sufficiently such that the polymer forming component can be mixed with the hardener component in fluid form prior to allowing the final composition to polymerize and / or solidify to yield the oilfield tracer material.

19. A method according to any one of claims 12 to 18, wherein the polymer forming component is an epoxy, a polyester, a polyol which generates a polyurethane in the oilfield tracer material.

20. An oilfield tracer material obtained according to the process of any of claims12 to 19.

21. A method of oilfield tracing, the method comprising: introducing an oil field tracer material according to any one of claims 1 to 7, a polymer bar according to claims 8 or 9, or a plurality of polymer beads according to claims 10 or 11 into a hydrocarbon reservoir, well, or wellbore; and monitoring for release of oil field chemical tracer from the oil field tracer material.

22. A method according to claim 21, wherein the oilfield tracer material is in the form of polymer beads which are injected into the hydrocarbon reservoir, well, or wellbore with proppant and frack fluid.

Images