A method for calculating the composition of formation gas in situ in a synthetic base drilling fluid for an actual oil well
By establishing the time-adsorption rate relationship of synthetic-based drilling fluid, the dynamic correction problem of gas logging of synthetic-based drilling fluid was solved, and the accurate inversion of gas logging components in the original formation was realized, improving the accuracy and efficiency of oil and gas reservoir identification and evaluation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGDONG UNIV OF PETROCHEMICAL TECH
- Filing Date
- 2026-01-07
- Publication Date
- 2026-05-29
AI Technical Summary
Under synthetic-based drilling fluid conditions, existing technologies exhibit systematic biases in gas logging results, failing to accurately reflect the true composition of the formation. This is particularly evident in cases of heavy components and short flowback times, where correction errors are significant, impacting the identification and evaluation of oil and gas reservoirs.
Through laboratory adsorption kinetics experiments, the time-adsorption rate relationship of synthetic-based drilling fluid for different hydrocarbon components was established, a dynamic correction model was constructed, and the original formation gas composition was calculated by combining the real-time flowback time in the field to achieve dynamic correction.
It has improved the accuracy and timeliness of gas logging interpretation, reduced engineering risks and ineffective operation costs, optimized the exploration and development process, and enhanced oil and gas field discovery and economic benefits.
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Figure CN122109355A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to, but is not limited to, the field of petroleum technology, and particularly relates to a method for calculating the composition of undisturbed formation gas in synthetic drilling fluid from actual oil wells. Background Technology
[0002] As global oil and gas exploration and development activities continue to extend into deepwater, ultra-deepwater, high-temperature and high-pressure (HPHT) formations, and environmentally sensitive areas, drilling engineering technology faces increasingly severe challenges. Against this backdrop, synthetic-based drilling fluids (SBDFs), due to their tunable properties and environmental advantages, are gradually becoming one of the important fluid systems in deepwater and complex well drilling operations. Traditional oil-based drilling fluids were widely used in the past due to their high lubricity and wall-keeping properties. However, with increasingly stringent environmental regulations and restrictions on their application in ecologically sensitive areas, synthetic-based drilling fluids have gained wider application due to their controllable molecular structure, low toxicity, and easier biodegradability. The base fluids of synthetic-based drilling fluids can be made from olefins, esters, ethers, or other synthetic organic compounds. These base oils can provide excellent wellbore stability, lubricity, and high-temperature robustness in different drilling environments, thus meeting the fluid requirements of challenging drilling operations.
[0003] During drilling, logging-while-drilling (LWD) is one of the most direct and important methods for discovering and evaluating oil and gas reservoirs. Its basic principle is to infer formation oil and gas characteristics by real-time monitoring of the hydrocarbon gas content and composition changes carried to the surface by the drilling fluid during circulation. Existing research has shown that the type, properties, and flow conditions of the drilling fluid have a significant impact on gas logging parameters. For example, experiments simulating the drilling process show that different drilling fluid systems have varying degrees of influence on total hydrocarbon detection values; this influence involves not only absolute concentration but also differences in component proportions.
[0004] For a long time, the academic and industrial communities have paid close attention to the impact of drilling fluids on the accuracy of gas logging. Non-polar oils in oil-based drilling fluids have a strong affinity for hydrocarbon gases. Based on the principle of "like dissolves like," these gases are more easily dissolved or adsorbed into the oil phase, thus altering the migration behavior of components within the bubbles. This causes the proportion of gas components entering the analyzer from the degasser to deviate from the original formation state. Numerous studies and engineering practices have summarized a series of empirical correction methods based on partition coefficients and absorption coefficients, attempting to correct the original field detection values using laboratory-measured data to restore a more accurate distribution of hydrocarbon components closer to the true formation. Some existing technologies also propose reducing the influence of reservoir properties, drilling fluid performance, and drilling parameters on gas logging data through comprehensive logging curve processing, thereby improving the geological significance of the interpretation.
[0005] However, existing technologies still have significant limitations. First, current research and engineering correction methods largely focus on traditional oil-based drilling fluid systems, with insufficient research on the impact mechanisms of synthetic-based drilling fluids. Mineral oil-based and synthetic-based drilling fluids differ fundamentally in their base oil chemical structure, molecular polarity, and physical properties, leading to different adsorption / dissolution selectivity and kinetic processes for various hydrocarbon components. Simply applying empirical models of oil-based systems directly to synthetic-based systems may introduce uncontrollable systematic errors and reduce the accuracy of gas logging data in reconstructing the true formation composition.
[0006] More critically, existing methods almost universally assume that the adsorption / dissolution process is a static process that reaches equilibrium instantaneously, neglecting the core kinetic factor of "time." In actual drilling conditions, there is a definite flowback time during the process of formation gas returning to the surface with drilling fluid, and the adsorption, dissolution, and desorption behaviors of different components within this time exhibit significant time dependence. Ignoring this dynamic process and using only a single saturated adsorption parameter for correction is equivalent to assuming that each component has already reached its equilibrium state at the bottom of the well during the flowback process, which is inconsistent with physical reality. This is especially true for heavy components or cases with short flowback times, where the correction error may be more significant. These technical limitations lead to potential systematic biases in the interpretation of reservoir fluid properties by existing gas logging results, restricting the development of accurate formation evaluation technology under synthetic-based drilling fluid systems.
[0007] Therefore, for the correction of gas logging data with synthetic-based drilling fluids, there is an urgent need to develop a quantitative correction method that can simultaneously consider the adsorption selectivity and flowback time kinetics of different gas components, so as to achieve dynamic and real-time correction of field gas logging data and improve the accuracy of interpretation. Summary of the Invention
[0008] To address the problems existing in the prior art, this invention provides a method for calculating the original formation gas composition in synthetic drilling fluid from actual oil wells.
[0009] This invention is implemented as follows: a method for calculating the undisturbed formation gas composition in synthetic-based drilling fluid from actual oil wells, the method comprising:
[0010] S1: Obtain synthetic-based drilling fluid and prepare standard gas samples from the study area. The components of the standard gas samples were determined by chromatography. ;
[0011] S2: Perform gaseous component saturation experiments on the sample, obtain gaseous component saturation curves, and clarify the gaseous adsorption saturation time and gaseous component content of each component. ;
[0012] S3: Conduct a standard gas adsorption experiment to determine the content of gas components in the synthetic-based drilling fluid after full adsorption of standard gas. ;
[0013] S4: Using standard gas as a reference, establish a formula for calculating the saturated adsorption rate (fn) of components in synthetic-based drilling fluids. By combining the adsorption saturation time of the gaseous components, a real-time adsorption rate of the gaseous components is established. ;
[0014] S5: Calculate the original formation gas composition in the synthetic drilling fluid of an actual oil well. .
[0015] Furthermore, S1 specifically includes:
[0016] The prepared gas mixture has a typical hydrocarbon component sequence, with a molar fraction of 10% methane. 10% ethane 1% propane 0.1% n-Butane 0.1% isobutane 0.1% n-Pentane 0.1% isopentane The composition uses nitrogen (N2) as the equilibrium medium; this design has clear geological implications: methane, as the dominant component, represents the dry gas end-member and is a major component of pyrolysis gas or highly mature natural gas; ethane and propane, as key intermediate molecular weight hydrocarbon wet gas components, Its significant content indicates that the gas belongs to a rich gas system and has a potential condensation tendency, usually associated with condensate gas reservoirs or associated gas; isomers of butane and pentane Although their absolute concentrations are low, their presence is crucial; these heavy hydrocarbon components are key parameters for defining the "humidity" of the system and calculating phase behavior, and their presence mainly simulates the impact of synthetic-based mud on gas logging.
[0017] The total system pressure set in the experiment was 10 MPa. This condition was used to simulate the medium to high pressure fluid environment experienced by underground reservoirs, and also to make it easier to extract the natural gas from the cylinders. In such high-pressure geological systems, the phase stability of hydrocarbon fluids is a core research topic in oil and gas exploration and development. According to the phase theory of oil and gas reservoir engineering, the phase state of any component in a mixture depends not only on its concentration, but more importantly on its partial pressure and dew point pressure at the current temperature. For pure components, it can be equivalent to the relative relationship between their saturated vapor pressures.
[0018] Furthermore, S2 specifically includes:
[0019] A pre-prepared 10% concentration standard gas was used as the simulated formation fluid; the composition of this standard gas is known to cover the complete series from C1 to nC5; the standard gas was continuously and slowly injected into a container containing synthetic-based drilling fluid through a precision flow control system; this design was intended to simulate the process by which formation fluid slowly and continuously enters the drilling fluid annulus through seepage and diffusion after the drill bit breaks the rock; at the outlet of the drilling fluid system, the composition and concentration of the extracted gas were measured in real time using an interval injection method and a high-precision gas chromatograph (GC).
[0020] Furthermore, S3 specifically includes:
[0021] After adsorption by the synthetic-based drilling fluid, the content of gas components after adsorption was obtained. The gas components exhibit dramatic and selective decay; and Although there was a decrease, the magnitude was much smaller than that of heavy hydrocarbons; starting from C3, the concentration dropped sharply: C3 dropped to 0.692%, iC4 / nC4 dropped to 0.046% / 0.037%, and iC5 / nC5 dropped even more dramatically to 0.024% / 0.018%.
[0022] Furthermore, S4 specifically includes:
[0023] Using standard gas as a reference, a formula for calculating the saturated adsorption rate (fn) of components in synthetic-based drilling fluid gas is established. In the formula: fn is the adsorption rate of the component measured by the synthetic-based drilling fluid gas, % The standard gas composition value is %; The values of gas components after adsorption in synthetic drilling fluid are given as %; and the real-time adsorption rate of gas components is established based on the adsorption saturation time of the gas components. .
[0024] Furthermore, S5 specifically includes:
[0025] On-site, the time it takes for the drilling fluid to return from the bottom of the well to the surface after encountering the surface layer is accurately recorded, which is the "flowback time" of the gas. By substituting the on-site flowback time of a certain component into its corresponding laboratory standard curve, the real-time concentration of that component in the drilling fluid at that specific moment can be read or calculated, and then its real-time adsorption rate fn(t) can be calculated.
[0026] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:
[0027] This invention aims to propose an innovative solution: through systematic laboratory adsorption kinetic experiments, quantitatively characterizing the "time-adsorption rate" relationship of synthetic-based drilling fluids for different hydrocarbon components, and constructing a dynamic correction model based on this. The ultimate goal of this method is to directly utilize the real-time measured content of contaminated gas logging components in the synthetic-based drilling fluid, along with known gas flowback times, to calculate the true content of gas logging components in the original formation using the established kinetic model. This is not only a technological shift from "static correction" to "dynamic restoration," but also elevates gas logging from a semi-quantitative monitoring tool to a quantitative interpretation system capable of accurately reversing reservoir fluid properties. The establishment and application of this method are expected to change the logic of oil and gas reservoir identification and evaluation under synthetic-based drilling fluid conditions, providing a more reliable data foundation for the precise exploration and efficient development of deep and complex reservoirs, ultimately leading gas logging technology into a dynamic, precise, and forward-looking new era.
[0028] This invention introduces time-dynamic variables to establish a real-time adsorption rate model for gas logging components, enabling the direct inversion of native formation gas logging components from real-time gas logging data of synthetic-based drilling fluids in unknown contamination states. This effectively avoids the heavy reliance of traditional methods on pre-obtained pure formation fluid standards or fixed empirical calibration charts. Furthermore, the method provided by this invention features a standardized experimental procedure, convenient model application, and strong operability and wide applicability in field operations. It has excellent prospects for widespread application in well logging interpretation for deepwater, complex formations, and synthetic-based drilling fluids.
[0029] (1) The expected benefits and commercial value of the technical solution of this invention after transformation are as follows: This method will directly improve the accuracy and timeliness of gas logging interpretation under synthetic-based drilling fluid conditions. By using the "time-adsorption rate" standard curve established in the laboratory, combined with the real-time flowback time in the field, the distortion of gas logging data can be dynamically corrected, and high-fidelity formation fluid can be restored. Component spectral analysis provides crucial data support for accurate fluid type identification (e.g., distinguishing between condensate gas and wet gas), rapid preliminary assessment of formation productivity, and subsequent sampling horizon decisions. Compared to waiting for lengthy laboratory PVT analysis or relying on inaccurate static corrections, this method, based on conventional gas logging equipment and a single systematic experiment, can achieve near real-time quantitative correction in the field, significantly reducing engineering risks (e.g., incorrect test horizon selection) and ineffective operational costs caused by fluid misjudgment. Its large-scale application can optimize exploration and development processes, improve the success rate of exploration wells and the decision-making efficiency of appraisal wells, ultimately creating significant value for maximizing the discovery and economic benefits of oil and gas fields.
[0030] (2) The technical solution of this invention fills a technical gap in the industry both domestically and internationally: This invention proposes and constructs for the first time a "gas logging component adsorption kinetic correction method" for synthetic-based drilling fluid systems. It creatively couples the gas backflow time with the dynamic adsorption curve of the components measured in the laboratory, and establishes a dynamic inversion model with the real-time adsorption rate fn(t) as the core. This solution breaks through the current technical framework in the industry that mainly relies on static "equilibrium adsorption rate" or correction based on oil-based drilling fluid empirical charts, and fills the technical gap in the field of gas logging of synthetic-based drilling fluids both domestically and internationally, which lacks a quantitative and kinetic pollution correction model, realizing a technical leap from "static equilibrium assumption" to "dynamic process correction".
[0031] (3) The technical solution of this invention solves a long-standing technical problem that people have long desired to solve but have never been able to: the solution successfully solves the long-standing coupling problem of "dynamic pollution quantification" and "original component inversion" in synthetic-based drilling fluid logging. Traditional correction methods ignore the time-dependent process of gas adsorption in drilling fluid, resulting in serious inaccuracies in gas logging data correction under short flowback times, especially for heavy components. This invention, through standardized adsorption kinetic experiments, clarifies the time scale required for each component to reach adsorption saturation and establishes its concentration function over time, thereby overcoming the key technical problem of how to accurately invert the fixed and unchanging formation real components (Cn formation) based on a pollution state (Cn synthetic base (real time)) that changes over time, providing a brand-new solution for real-time and accurate fluid evaluation.
[0032] (4) The technical solution of this invention overcomes technical biases: This invention overcomes two major technical biases that have long existed in the industry: First, it is believed that the adsorption / dissolution effect of drilling fluid on gas can be characterized by a final, fixed saturation adsorption rate to meet the correction requirements. This method proves through rigorous experimental data that the adsorption rate of each component is a function of time before reaching saturation, and the time constants of different components are significantly different, thus establishing the necessity of "dynamic correction" and overcoming the technical bias that "static correction" is sufficient to meet the engineering accuracy requirements. Second, it is believed that in the absence of pure formation gas samples, it is impossible to perform accurate, physical mechanism-based quantitative correction of the pollution effect of synthetic-based drilling fluid, and only qualitative or semi-quantitative empirical estimation can be performed. This solution establishes a benchmark scale (fn) for the pollution effect by introducing standard gas with known components for systematic experiments, and then performs dynamic extrapolation through the time variable (t), realizing the quantitative correction of pollution of any unknown formation gas without prior knowledge of the specific formation gas composition, breaking the traditional mindset that must rely on pure samples of the target formation. Attached Figure Description
[0033] Figure 1This is a flowchart of a method for calculating the composition of undisturbed formation gas in synthetic drilling fluid from an actual oil well, provided by an embodiment of the present invention.
[0034] Figure 2 These are standard gas adsorption saturation experimental data curves (methane, ethane, propane) provided in the embodiments of the present invention.
[0035] Figure 3 These are standard gas adsorption saturation experimental data curves (butane, pentane) provided in the embodiments of the present invention.
[0036] Figure 4 This is a graph showing the measured saturation time and gas composition of synthetic-based drilling fluid provided in an embodiment of the present invention.
[0037] Figure 5 This is a diagram of the on-site gas logging component prediction model provided in an embodiment of the present invention. Detailed Implementation
[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0039] To address the long-standing industry problem of "falsely low heavy hydrocarbon levels, distorted composition, and inability to invert" in gas logging results under synthetic-based drilling fluid conditions, existing technologies largely remain at the level of empirical correction or qualitative judgment, failing to meet the needs of refined evaluation of unconventional oil and gas and condensate gas reservoirs. Synthetic-based drilling fluids... The hydrocarbons mentioned above exhibit significant selective dissolution and adsorption effects, causing gas logging values to no longer be equivalent to the original formation gas composition. This directly leads to misjudgments of reservoir type, distortion of humidity parameters, and deviations in phase analysis. This method, based on the premise that "the adsorption behavior of synthetic-based drilling fluids and gas components can be quantitatively characterized," establishes a quantitative calculation path capable of retrieving the original formation gas logging components from both experimental and theoretical perspectives. This fundamentally solves the problem of uncorrectable gas logging data under synthetic-based systems.
[0040] In the implementation of this method, a multi-component standard gas system with clear geological significance is introduced to establish a molecular-scale correspondence between experimental conditions and real reservoir fluids. The standard gas covers the complete hydrocarbon sequence from CH4 to C5 and is fully contacted with synthetic-based drilling fluid under high pressure. Its purpose is not simply adsorption testing, but to simulate the real distribution behavior of hydrocarbons with different carbon numbers in the drilling fluid system. Through continuous gas injection, dynamic degassing, and real-time chromatographic detection, the complete evolution process of each gas component from initial entry to gradual saturation is obtained, thus avoiding the deficiency of traditional static experiments in reflecting the coupling relationship of "time-concentration-adsorption" during drilling.
[0041] From a physicochemical perspective, the influence of synthetic-based drilling fluids on gases is essentially a nonlinear process jointly controlled by dissolution, interfacial adsorption, and phase partitioning, and this process is highly sensitive to molecular weight. Experimental results show that C1 and C2 components are predominantly gaseous with limited adsorption effects, while C3 and higher components exhibit significant preferential adsorption characteristics due to their molecular polarity, critical properties, and enhanced compatibility with the base oil. This method normalizes the complex microscopic processes into calculable proportional relationships by defining the core parameter of "saturated adsorption rate of gas-based components," making different components comparable within the same theoretical framework and providing a unified physical basis for subsequent inversion.
[0042] At the parameter modeling level, using standard gas component values as a reference, adsorption rates and their real-time evolution functions for gas components were constructed. The limiting adsorption state was determined through saturated adsorption experiments, and a real-time adsorption rate function was introduced in conjunction with the time dimension, making the adsorption behavior no longer a static constant but a continuous function that changes with contact time. This approach effectively solves the problem of inconsistent calibration of gas measurement values under different depths and flowback times during field drilling, enabling the transferability of laboratory calibration results to field conditions.
[0043] In practical oil well applications, this method identifies the state of gas logging values at any given time by correlating the precisely recorded flowback time in the field with the adsorption kinetic curves established in the laboratory. The gas logging components of the synthetic-based drilling fluid measured in the field are not directly used for geological interpretation, but rather as inversion inputs. After real-time adsorption rate correction, they are restored to the corresponding original formation gas logging components. This process does not rely on empirical coefficients or require prior assumptions about formation type, avoiding interference from subjective human judgment and significantly improving the reliability of gas logging data.
[0044] From an industrial application perspective, this method enables the transformation of gas logging under synthetic-based drilling fluid conditions from "qualitative indication" to "quantitative inversion," directly serving key engineering decision-making processes such as condensate gas reservoir identification, gas-oil ratio determination, humidity parameter calculation, and phase analysis. By establishing a standardized experimental-calculation-field coupling process, data from different blocks and drilling systems are made comparable, providing a replicable and scalable technical path for the refined evaluation of unconventional oil and gas, demonstrating clear engineering application value and promising prospects for wider application.
[0045] In one exemplary embodiment, the synthetic drilling fluid may be an ester-based synthetic drilling fluid, an ether-based synthetic drilling fluid, an alkylated synthetic drilling fluid, or a mixture thereof in any proportion, preferably with a density of 1.2–1.8 g / cm³ and an apparent viscosity of [missing information]. Ester-based synthetic drilling fluids within the specified range. The drilling fluid may contain conventional additives such as emulsifiers, lubricants, filtration reducers, plugging agents, and weighting materials; their types and contents do not constitute a substantial limitation of this method.
[0046] Under laboratory conditions, a standard gas of known composition is introduced into the synthetic drilling fluid. The standard gas may optionally include at least one of methane, ethane, propane, n-butane, isobutane, n-pentane, and isopentane; preferably, its volume fraction is: methane 8–12%, ethane 8–12%, propane 0.5–2%, butane 0.05–0.2%, pentane 0.05–0.2%, with the remainder being nitrogen or helium as a balance gas. The standard gas is continuously introduced into the drilling fluid at a flow rate of 50–300 mL / min, and adsorption experiments are conducted at a pressure of 5–20 MPa and a temperature of 30–90°C to simulate the downhole working environment.
[0047] During continuous gas intake, the concentrations of various gas components in the drilling fluid are monitored online or intermittently. The monitoring equipment can be a gas chromatograph, mass spectrometer, or infrared gas analyzer. When the concentration of each gas component stabilizes over time, the system is considered to have reached adsorption saturation, and the concentration detected at this point is defined as the saturated adsorption concentration of the corresponding gas component. By comparing the difference or proportional relationship between the initial concentration of the standard gas and the saturated adsorption concentration, the saturated adsorption rate of that gas component in the synthetic-based drilling fluid can be calculated.
[0048] Furthermore, to characterize the dynamic changes in the adsorption process, multiple time sampling points can be set during the adsorption process to establish a real-time adsorption rate function of the gaseous components as a function of time. This function can be optionally an exponential function, a logarithmic function, a piecewise linear function, or an empirical function obtained by fitting experimental data.
[0049] In field applications, the first step is to record the flowback time of the drilling fluid from the bottom of the well to the surface. This flowback time is then mapped to an adsorption rate-time curve established in the laboratory. The real-time adsorption rate corresponding to this flowback time is determined through interpolation or function evaluation. Subsequently, the real-time adsorption rate is used to invert and correct the concentrations of gas components measured in the field, thereby obtaining a more accurate concentration of components closer to the original formation gas.
[0050] In another embodiment, the corrected concentration of gas components can be further used to calculate formation gas humidity parameters, wet-dry ratio, and heavy hydrocarbon ratio, or for engineering applications such as reservoir type identification, phase analysis, and reservoir evaluation.
[0051] like Figure 1 As shown, this embodiment of the invention provides a method for calculating the original formation gas composition in synthetic-based drilling fluid from actual oil wells. The method includes:
[0052] S1: Sample Acquisition and Preparation of Standard Gases
[0053] The prepared gas mixture has a typical hydrocarbon component sequence, with a molar fraction ratio of 10% methane ( ), 10% ethane ( ), 1% propane ( ), 0.1% n-butane ( ), 0.1% isobutane ( ), 0.1% n-pentane ( ), 0.1% isopentane ( ), and with nitrogen ( The composition serves as the equilibrium medium. This design has a clear geological basis: methane, as the dominant component, represents the dry gas end-member and is a major component of pyrolysis gas or highly mature natural gas. Ethane and propane serve as key intermediate molecular weight hydrocarbons (wet gas components). The significant content of this gas indicates that it belongs to a rich gas system and has a potential tendency to condense, usually associated with condensate gas reservoirs or associated gas in oil and gas fields. Isomers of butane and pentane ( Although their absolute concentrations are low, their presence is crucial. These heavy hydrocarbon components are key parameters for defining the system's "humidity" and calculating phase behavior. Their presence primarily simulates the impact of synthetic-based mud on gas logging. The actual mixing ratios are shown in Table 1.
[0054] The total system pressure was set at 10 MPa in the experiment to simulate the medium to high pressure fluid environment experienced by underground reservoirs, and also to facilitate the extraction of natural gas from the cylinders. In such high-pressure geological systems, the phase stability of hydrocarbon fluids is a core research topic in oil and gas exploration and development. According to the phase theory of oil and gas reservoir engineering, the phase state of any component in a mixture depends not only on its concentration, but more importantly on the relative relationship between its partial pressure and its dew point pressure at the current temperature (which, for a pure component, can be equivalent to its saturated vapor pressure).
[0055] Table 1. Experimental Results of Synthetic-Based Drilling Fluid
[0056] S2: Perform gas component saturation experiments on the sample, obtain gas component saturation curves, and determine the gas component saturation time and adsorption saturation lower limit for each component.
[0057] A pre-prepared 10% concentration standard gas was used as the simulated formation fluid. The composition of this standard gas is known (Table 1), covering fluids from... arrive The complete series. A standard gas is continuously and slowly injected into a container holding synthetic-based drilling fluid via a precision flow control system. This design simulates the process by which formation fluids slowly and continuously enter the drilling fluid annulus through seepage and diffusion after the drill bit breaks the rock. At the outlet of the drilling fluid system, a high-precision gas chromatograph (GC) is used to measure the composition and concentration of the extracted gas in real time using an interval injection method.
[0058] Experimental data on the adsorption gas saturation of different components were obtained (Table 1, Table 2), and a graph showing the relationship between gas measurement time and the content of gas components was also obtained. Figure 2 , Figure 3 This helps to clarify the content of each component in the gaseous sample at different adsorption saturation times. , for real-time adsorption rate This provides a basis for the calculation.
[0059] Meanwhile, due to limitations in the experimental conditions and The saturation time was not measured, but to verify the universality of the rule, the first 6 components ( to The saturation time and carbon number of a carbon atom are subjected to nonlinear regression analysis (such as exponential or power function fitting). The fitted curve is then used to extrapolate and predict... The saturation time (referring generally to pentane isomers) is approximately 3 hours at most. This prediction provides a crucial timescale reference for long-term on-site monitoring of aftereffect gas. Figure 4 ).
[0060] Table 2 Measured saturation time of synthetic-based drilling fluid
[0061]
[0062] S3: Conduct a standard gas adsorption experiment to determine the content of gas components in the synthetic-based drilling fluid after full adsorption of standard gas. .
[0063] After adsorption by the synthetic-based drilling fluid, the content of gas components after adsorption was obtained. The gas components exhibited a dramatic and selective decay (Table 3). and Although there was a decrease (to 9.099% and 8.812% respectively), the decline was much smaller than that of heavy hydrocarbons. From Initially, the concentration dropped precipitously: It dropped to 0.692%. It dropped to 0.046% / 0.037%, while It dropped significantly to 0.024% / 0.018%. The proportion of recombinant components also decreased from 0.02% to 0.01% (Table 3).
[0064] Table 3 Experimental data on the degree of adsorption of standard gas
[0065] S4: Using standard gas as a reference, establish a formula for calculating the saturated adsorption rate (fn) of components in synthetic-based drilling fluids. By combining the adsorption saturation time of the gaseous components, a real-time adsorption rate of the gaseous components is established.
[0066] A formula for calculating the saturated adsorption rate (fn) of components in synthetic drilling fluid gas is established based on standard gas. In the formula: fn is the adsorption rate of the component measured by the synthetic-based drilling fluid gas, %; The standard gas composition value is %; The percentage of gaseous components after adsorption by synthetic drilling fluid is given. Based on the adsorption saturation time of the gaseous components, a real-time adsorption rate of the gaseous components is established. .
[0067] S5: Calculate the original formation gas composition in the synthetic drilling fluid of an actual oil well. .
[0068] On-site, the time it takes for the drilling fluid to return from the bottom of the well to the surface after encountering the show formation is precisely recorded; this is known as the "flowback time" of the gas. By substituting the on-site flowback time of a specific component into its corresponding laboratory standard curve, the real-time concentration of that component in the drilling fluid at that specific moment can be read or calculated, and its real-time adsorption rate can then be calculated. The content of gas components measured on-site was combined with the data. The gas concentration measured on-site was corrected to restore it to the true content of the formation. ( Figure 5 ).
[0069] Example 1
[0070] A commonly used synthetic drilling fluid sample was selected for a multi-component gas adsorption experiment under isothermal and high-pressure conditions. Before the experiment, the drilling fluid underwent degassing pretreatment to eliminate background interference. Subsequently, a mixed standard gas containing methane to pentane was prepared according to a predetermined ratio and slowly introduced into the drilling fluid through a precision flow control system, allowing the gas to continuously infiltrate and fully contact the drilling fluid. During the experiment, the extracted gas was collected in real time, and the concentration of each component was continuously monitored.
[0071] As the gas inlet time increases, the concentrations of each gas-detecting component gradually change. When the fluctuations in the test results are less than a set threshold after multiple consecutive tests, the system is considered to have reached a stable adsorption state. By comparing the initial standard gas concentration with the detected concentration under stable conditions, the saturated adsorption characteristics of each gas-detecting component in the synthetic-based drilling fluid are obtained, providing basic data for subsequent inversion calculations.
[0072] Example 2
[0073] Based on the above experimental system, the adsorption kinetics of hydrocarbons with different carbon numbers were studied in detail. The focus was on the concentration changes of propane, butane, and pentane in synthetic-based drilling fluids, and gas logging data with higher temporal resolution were obtained by shortening the sampling time interval.
[0074] By mathematically fitting the concentration-time curves of each heavy hydrocarbon component, the relationship between its adsorption rate and contact time is established, thereby forming a functional model that can describe the real-time adsorption state of the gaseous components, transforming the adsorption process from a qualitative description to a quantitative expression.
[0075] Example 3
[0076] The adsorption model established in the laboratory was applied to data processing in an actual drilling section. During the field operation, the flowback time of the drilling fluid from the bottom of the well to the surface was continuously recorded, and the real-time detection values of each component output by the gas logging system were collected simultaneously.
[0077] Based on the correspondence between the backflow time and the laboratory adsorption time curve, the adsorption state of each gaseous component at the backflow time is determined, the on-site detection concentration is corrected, and the original formation gaseous components at the corresponding depth are obtained by inversion, thus realizing the quantitative recovery of on-site gaseous data.
[0078] Example 4
[0079] To address the impact of differences in the characteristics of synthetic-based drilling fluids from different sources, adsorption experiments were repeatedly conducted on various synthetic-based systems. Comparison revealed differences in the adsorption rates and saturation levels of each gas-based component in different systems, but all exhibited stable and repeatable variation patterns.
[0080] Based on this difference, corresponding adsorption model parameter libraries are established. When applied in the field, the appropriate model is selected according to the type of drilling fluid to achieve targeted correction of gas measurement data and improve the applicability of the method under different engineering conditions.
[0081] Example 5
[0082] The inverted original formation gas parameters were used to evaluate formation fluid properties, calculating gas humidity parameters and heavy hydrocarbon content, and comparing the results with those from gas testing and sampling analysis. The results show that the corrected gas parameters are highly consistent with the actual formation fluid characteristics in terms of component proportions and trends.
[0083] This implementation method verifies the effectiveness of the method in correcting distortion of gas logging data under synthetic drilling fluid conditions, providing a reliable data foundation for condensate gas reservoir identification, gas-oil ratio analysis, and phase determination, and has clear engineering application value.
[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for calculating the undisturbed formation gas composition in synthetic-based drilling fluid from actual oil wells, characterized in that, include: Obtain the baseline concentration values of each gas component in the standard gas sample; In a synthetic-based drilling fluid system, the adsorption saturation state of each gas-detecting component was established, and the corresponding saturation adsorption rate of the gas-detecting component was obtained. Based on the real-time detection concentration of the gaseous component and the saturated adsorption rate, a real-time adsorption rate function for the gaseous component is constructed. Using the real-time adsorption rate function, the gas composition of the synthetic-based drilling fluid measured in the field is corrected, and the concentration of the original formation gas composition is obtained by inversion.
2. The method according to claim 1, characterized in that, The gaseous components include at least one of methane, ethane, propane, butane, and pentane.
3. The method according to claim 1, characterized in that, The saturated adsorption rate of the gaseous components is calculated by the difference between the concentration of the standard gas component and the concentration of the adsorbed component after the standard gas reaches a stable adsorption state in the synthetic-based drilling fluid.
4. A method for establishing the adsorption rate of gas-based components in synthetic drilling fluid, characterized in that, include: Introduce standard gases with known component concentrations into synthetic-based drilling fluids; Under continuous air intake conditions, the component concentrations of the extracted gas are dynamically monitored; When the concentration of a gaseous component reaches a stable state, the saturated adsorption concentration of that gaseous component is determined. Based on the standard gas component concentration and saturated adsorption concentration, the saturated adsorption rate of the gas component is established. By combining the adsorption time, a real-time adsorption rate function of the gaseous components as a function of time is constructed.
5. The method according to claim 4, characterized in that, The standard gas contains 10% methane, 10% ethane, 1% propane, 0.1% n-butane, 0.1% isobutane, 0.1% n-pentane, 0.1% isopentane, and the remainder is nitrogen.
6. The method according to claim 4, characterized in that, The adsorption experiment was conducted under a pressure of 10 MPa.
7. The method according to claim 4, characterized in that, The real-time adsorption rate function is determined by the ratio between the real-time detection concentration of the gaseous component and the reference concentration of the standard gas.
8. A method for correcting the composition of synthetic-based drilling fluid gas based on flowback time, characterized in that, include: Record the time it takes for drilling fluid to flow back from the bottom of the well to the surface; The backflow time is mapped to the adsorption time curve of gaseous components established in the laboratory; Determine the real-time adsorption rate of the gaseous components corresponding to the backflow time; The real-time adsorption rate is used to correct the on-site measured gas components to obtain the original formation gas components.
9. The method according to claim 8, characterized in that, The real-time adsorption rate corresponding to the backflow time is obtained by interpolation calculation.
10. The method according to claim 8, characterized in that, The corrected original formation gas measurement components are used for formation gas humidity parameter calculation or phase analysis.