plunger core high temperature high pressure reservoir fluid sensitivity mudflood method

Abstract

This invention discloses a cuttings-turbidity method for assessing reservoir fluid sensitivity in high-temperature and high-pressure reservoirs, addressing the challenges of high core drilling costs in high-temperature and high-pressure reservoirs, the difficulty in obtaining complete core plungers in fractured reservoirs, and the limitations of laboratory evaluation methods in simulating reservoir conditions. This invention uses cuttings as a substitute for core plungers in experiments. By screening reservoir cuttings samples, and based on the principle of reservoir particle detachment and dispersion after the interaction of rock minerals with fluids of different properties, the change in cuttings mass and fluid turbidity before and after the interaction is measured. This quantitatively characterizes the reservoir fluid sensitivity induced by working fluid intrusion and establishes an evaluation index based on cuttings to assess the reservoir sensitivity induced by working fluid intrusion. This invention can simulate the actual high-temperature and high-pressure environment of reservoirs, considering the changes in mass and turbidity of cuttings before and after the interaction with fluids, and quantitatively evaluate the reservoir fluid sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas extraction technology, especially the high-temperature and high-pressure reservoir fluid sensitivity cuttings-turbidity method, which is extremely scarce in plunger rock samples and is mainly used to evaluate reservoir fluid sensitivity. Background Technology

[0002] As oil and gas resources are exploited, the difficulty of extraction is increasing, and more and more high-temperature and high-pressure reservoirs are waiting to be exploited. This leads to serious engineering accidents such as well leakage and well collapse, which seriously affect the oil extraction process. The main reason for this is the failure to better understand the fluid sensitivity of the reservoirs and the lack of knowledge about the reservoirs.

[0003] Accurate analysis and understanding of reservoir fluid sensitivity and its damage mechanisms are prerequisites and key factors for implementing reservoir protection measures. Different damage mechanisms often exhibit similar damage characteristics and phenomena. Failure to accurately determine the damage mechanism may result in either inability to improve reservoir damage or, in severe cases, serious engineering accidents. Therefore, it is essential to adopt correct and accurate reservoir sensitivity assessment methods, correctly analyze reservoir damage mechanisms, and implement appropriate reservoir protection measures.

[0004] Reservoir sensitivity is a crucial aspect of oil and gas reservoir protection, encompassing fluid sensitivity, stress sensitivity, and phase trapping. Fluid sensitivity is paramount, as fluid-sensitive damage arises from physical and chemical reactions between reservoir rocks / fluids and external working fluids, leading to a significant decrease in reservoir permeability. The primary mechanism causing fluid-sensitive damage involves mineral contraction, expansion, detachment, dispersion, and migration, resulting in blockage of seepage channels.

[0005] The industry standard method (SY / T5358-2010) is a representative steady-state evaluation method. The experiment is carried out at room temperature, and fluid is driven into the rock sample at a constant flow rate or constant pressure. The sensitivity of the reservoir is evaluated by comparing the changes in permeability of the rock sample after different fluids are driven in. This standard is only applicable to the sensitivity evaluation of clastic rock reservoirs with air permeability > 1 mD under a confining pressure of 3 MPa.

[0006] Using industry-standard methods to evaluate the fluid sensitivity of high-temperature and high-pressure reservoir cores can lead to numerous problems, including low experimental accuracy, high requirements for experimental equipment pressure and fluid measurement precision, and long evaluation times, because these methods do not consider the high temperature and pressure factors. Furthermore, the high cost of core sampling in high-temperature and high-pressure reservoirs, and the difficulty in obtaining sufficient core samples from fractured reservoirs to support the industry-standard methods for evaluating fluid sensitivity, necessitates exploring a new evaluation approach. This approach uses rock cuttings to establish reservoir sensitivity evaluation indices instead of core permeability loss rates, while also considering the high temperature and pressure factors. Simultaneously, it allows for the use of a single instrument to test multiple samples, significantly shortening the laboratory evaluation time and solving the problems of insufficient core samples and lengthy evaluation periods. Summary of the Invention

[0007] The purpose of this invention is to provide a cuttings-turbidity method for assessing reservoir fluid sensitivity in situations where plunger rock samples are extremely scarce. This method involves screening experimental samples to select particles within a specific size range, weighing a certain mass of cuttings for testing, applying reservoir pressure to the reaction vessel, using a fluid gradient, and measuring reservoir temperature. This allows for the simulation of reservoir temperature and pressure conditions for sensitivity evaluation even when downhole core samples are insufficient. This method characterizes the reservoir fluid sensitivity by measuring the mass loss rate of the cuttings, thus achieving the goal of evaluating reservoir fluid sensitivity. The specific steps are as follows:

[0008] S1: Collect rock cuttings samples returned from the wellhead during drilling, wash with methanol for salt removal, dry, and then screen out rock cuttings samples within a certain particle size range. Based on the pH or mineralization gradient n of the sensitive fluid, weigh n portions of m1 rock cuttings.

[0009] S2: The rock fragments from S1 are placed into n reaction containers containing experimental fluids, stirred thoroughly, and allowed to stand for a certain period of time. After measuring the turbidity c1, the containers are then sealed and tightened. The fluids are specific solutions with a certain concentration gradient, such as simulated formation water, acid solutions, and alkaline solutions.

[0010] S3: Use a nitrogen cylinder to pressurize the reaction vessel containing the experimental sample to the reservoir pressure, and place the reaction vessel in a rolling heating furnace, set the temperature to the reservoir temperature, and heat and roll it.

[0011] S4: After a certain period of constant temperature rolling, remove the reaction vessel from the rolling heating furnace, allow it to cool naturally to room temperature, and then release the remaining gas in the reaction vessel.

[0012] S5: Pour the liquid from the reaction vessel in S4 onto different sieves and collect the fluids in beakers. After wet washing the sieves in a water tank filled with tap water, dry them in a forced-air constant-temperature drying oven, remove them to cool, and seal them in dry air for a certain period of time. Then weigh them separately (m2).

[0013] S6: Stir the collected fluid thoroughly, let it stand for a certain period of time, and then measure the turbidity c2;

[0014] S7: The reservoir fluid sensitivity index S is calculated using the following formula to evaluate the reservoir fluid sensitivity:

[0015]

[0016] When S > 98%, the sensitivity is low to low.

[0017] When 95% < S ≤ 98%, the sensitivity is moderate to weak.

[0018] When 90% < S ≤ 95%, the sensitivity is moderately high.

[0019] When S≤90%, the sensitivity is high.

[0020] The advantages and benefits of this invention are as follows:

[0021] (1) In some well areas where it is difficult to obtain downhole cores, such as deep wells, ultra-deep wells, and offshore drilling, the number of downhole cores in these areas cannot meet the industry standard requirements for reservoir sensitivity assessment. Or in some reservoirs where core extraction is difficult, such as fractured reservoirs and high-temperature and high-pressure reservoirs. The method of this invention directly uses rock cuttings to assess the degree of reservoir sensitivity damage without the need for downhole cores. It solves the problem of not being able to assess sensitivity damage due to the lack of available cores.

[0022] (2) This invention is also applicable to tight reservoirs, where the traditional reservoir sensitivity evaluation method—core displacement method—is completely inapplicable. It solves the problem of being unable to evaluate sensitivity due to reservoir characteristics.

[0023] (3) This invention fully considers the actual reservoir environment. By pressurizing and heating, it simulates the real reservoir environment and combines the rock cuttings mass recovery rate with the fluid turbidity change rate as evaluation indicators. The measured results can reflect the real reservoir conditions and have good guiding significance for engineering practice.

[0024] (4) This invention uses rock cuttings to evaluate reservoir sensitivity, which is simple to operate, highly feasible, and cost-saving compared to core flow analysis. Attached Figure Description

[0025] Figure 1 This invention relates to a device for a high-temperature, high-pressure reservoir fluid-sensitive cuttings-turbidity method, which is extremely scarce in plunger rock samples.

[0026] In the diagram: 1. Vent valve, 2. Fastening bolt, 3. Reaction vessel, 4. Fluid of a certain concentration, 5. Rock cuttings. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] The high-temperature, high-pressure reservoir fluid-sensitive cuttings-turbidity method, which is extremely rare in plunger rock samples, includes the following steps (see...). Figure 1 ):

[0029] ① Rock cuttings samples were collected from the wellhead during drilling at an offshore well in the Bohai Bay Basin. Methanol was used for salt washing. After cleaning and drying, rock cuttings samples with a particle size between 6 mesh and 10 mesh were screened out. Five portions, each m1, were weighed. 1 m1 2 m1 3 m1 4 m1 5 Rock fragments.

[0030] ② The rock cuttings were placed into five reaction containers, each containing formation water, 3 / 4 formation water, 1 / 2 formation water, 1 / 4 formation water, and distilled water, respectively. The solid-liquid mass ratio was 1:100, and the formation water salinity was 200,000 mg / L. After thorough stirring and standing for 10 minutes, the turbidity c1 was measured. 1 c1 2 c1 3 c1 4 c1 5 Then tighten the lid.

[0031] ③ Use a nitrogen cylinder to pressurize the reaction vessel containing the experimental sample to the reservoir pressure of 46 MPa, and place the reaction vessel in a rolling heating furnace, set the temperature to the reservoir temperature of 130°C, and heat and roll.

[0032] ④ After 16 hours of constant temperature rolling, remove the reaction vessel from the rolling heating furnace, allow it to cool naturally to room temperature, and then release the remaining gas in the reaction vessel.

[0033] ⑤ Pour the liquid from the reaction vessel onto five 100-mesh sieves and collect the fluid in beakers. After wet-washing the sieves in a water bath for 1 minute, place them in a 50°C forced-air drying oven for 8 hours. Remove and cool, then seal and allow to stand in dry air for 24 hours. Finally, weigh each sieve (m²). 1 m2 2 m2 3 m2 4 m2 5 ;

[0034] ⑥ Stir the fluid thoroughly, let it stand for 10 minutes, and then measure the turbidity c2. 1 c2 2 c2 3 c2 4 c2 5 ;

[0035] ⑦ Calculate the reservoir sensitivity index S using the following formula to evaluate the degree of reservoir damage:

[0036]

[0037] Experimental results show that the reservoir salt sensitivity index S is 92%, indicating a moderate to strong sensitivity. To verify the scientific validity of this method, a core plunger-salt sensitivity evaluation experiment was conducted using the well's downhole core. The experimental results show that the salt sensitivity is moderate to strong, indicating the high reliability of reservoir damage assessment results obtained using cuttings.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A PIR high temperature high pressure reservoir fluid sensitivity mudfinge- turbidity method characterized by Includes the following steps: S1: Collect rock cuttings samples returned from the wellhead during drilling, clean and dry them, screen rock cuttings samples within a certain particle size range, and weigh n portions of m1 rock cuttings according to the pH or mineralization gradient n of the sensitive fluid. S2: The rock fragments in S1 are placed into n reaction containers containing experimental fluids, stirred thoroughly, and allowed to stand for a certain period of time. After measuring the turbidity c1, the containers are then sealed and tightened. The fluids are specific solutions with a certain concentration gradient. S3: Use a nitrogen cylinder to pressurize the reaction vessel containing the experimental sample to the reservoir pressure, and place the reaction vessel in a rolling heating furnace, set the temperature to the reservoir temperature, and heat and roll it. S4: After a certain period of constant temperature rolling, remove the reaction vessel from the rolling heating furnace, allow it to cool naturally to room temperature, and then release the remaining gas in the reaction vessel. S5: Pour the liquid in the reaction vessel in S4 onto different sieves and collect the liquid in a beaker; after wet washing the sieves in a water tank filled with tap water, dry them in a forced-air constant temperature drying oven, take them out to cool, and seal them in dry air for a certain period of time, and then weigh them separately (m2). S6: Stir the collected fluid thoroughly, let it stand for a certain period of time, and then measure the turbidity c2; S7: Calculate the reservoir working fluid damage index S using the following formula to evaluate the degree of reservoir damage: 。 2. The high-temperature, high-pressure reservoir fluid-sensitive cuttings-turbidity method for plunger rock samples, which is extremely scarce as described in claim 1, is characterized in that... In steps S2 and S6, the settling time is 9-11 minutes.

3. The high-temperature, high-pressure reservoir fluid-sensitive cuttings-turbidity method for plunger rock samples, which is extremely scarce as described in claim 1, is characterized in that... In step S2, the amount of experimental fluid satisfies a solid-liquid mass ratio of 1:

100.

4. The high-temperature, high-pressure reservoir fluid-sensitive cuttings-turbidity method for plunger rock samples, which is extremely scarce as described in claim 1, is characterized in that... In step S6, when S > 98%, the sensitivity is zero to weak; when 95% < S ≤ 98%, the sensitivity is moderately weak; when 90% < S ≤ 95%, the sensitivity is moderately strong; and when S ≤ 90%, the sensitivity is strong.

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