Permeability Oil Research Articles

Experimental study on the mechanism of five point pattern refracturing for vertical & horizontal wells in low permeability and tight oil reservoirs

Low permeability oil reservoir has the characteristics of low porosity and low permeability. The initial fracturing can effectively improve the recovery of the reservoir, but the physical mechanism of refracturing to improve the recovery is still lack of systematic research. In this paper, the refracturing effect of low permeability reservoirs under the condition of five point well pattern is clarified; the refracturing mechanism of vertical-horizontal well combination is revealed; the reservoir production performance characteristics under different soak time conditions are analyzed. It is found that: (a) after 1st fracturing, the area between the two fractures still has a high residual oil, which is the material basis for refracturing. (b) After refracturing, there are secondary fractures connecting the main fractures. The crude oil in the low permeability reservoir can flow not only to the main fracture and horizontal wellbore, but also to the secondary fractures. This leads to the effective reduction of oil saturation between the main fractures. (c) The influence of soak time on cumulative oil production is obvious. With the increase of soak time, the cumulative oil production increases significantly.

Experimental study on water flooding mechanism in low permeability oil reservoirs based on nuclear magnetic resonance technology

Low permeability oil reservoirs are characterized by complex pore-throat structure and complex mechanism of oil and water storage and transmission. At present, the research on cross-scale characteristics of pore-throat structure in low permeability reservoirs needs to be strengthened, and the research on oil-water evolution characteristics needs to be improved. In this paper, based on NMR method, different “porosity-permeability-original oil saturation” coupling evaluation systems are constructed, the study on oil and water distribution characteristics at different water flooding stages has been carried out, and the distribution mechanism of residual oil in pores with different sizes is analyzed. It is found out that: (a) the higher the core permeability, the lower the displacement pressure; the lower the core permeability, the higher the displacement pressure. (b) The T2 spectrum shows that micropores, mesopores and macropores in core samples are well developed. (c) The morphology of T2 spectrum can be divided into three types: high right peak and low left peak, high left peak and low right peak, and basically equal left and right peaks. In addition, under saturated oil conditions, medium and large pores are the main oil storage spaces. (d) There are three factors affecting the water flooding efficiency: the influence of micro-fractures, the influence of pore-throat heterogeneity and the influence of the degree of producing pore-throat.

The Impact of 3D Prism Cavity for Enhanced Oil Recovery Using Different Nanomaterials.

Enhanced oil recovery (EOR) has been offered as an alternative to declining crude oil production. EOR using nanotechnology is one of the most innovative trends in the petroleum industry. In order to determine the maximum oil recovery, the effect of a 3D rectangular prism shape is numerically investigated in this study. Using ANSYS Fluent software(2022R1), we develop a two-phase mathematical model based on 3D geometry. This research examines the following parameters: flow rate Q = 0.01-0.05 mL/min, volume fractions = 0.01-0.04%, and the effect of nanomaterials on relative permeability. The result of the model is verified with published studies. In this study, the finite volume method is used to simulate the problem, and we run simulations at different flow rates while keeping other variables constant. The findings show that the nanomaterials have an important effect on water and oil permeability, increasing oil mobility and lowering IFT, which increases the recovery process. Additionally, it has been noted that a reduction in the flow rate improves oil recovery. Maximum oil recovery was attained at a 0.05 mL/min flow rate. Based on the findings, it is also demonstrated that SiO2 provides better oil recovery compared to Al2O3. When the volume fraction concentration increases, oil recovery ultimately increases.

Effects of salinity alternation on relative permeability and capillary pressure as determined from steady-state-transient test

This paper aims the development of a new laboratory method for the simultaneous determination of phase relative permeability (Kr) and capillary pressure (Pc) for low salinity (LS) waterflooding. The proposed method is based on the so-called steady-state-transient (SSTT) method that uses steady-state and transient coreflood data, which allows calculating Kr and Pc from the same coreflood. A novel mathematical modelling is developed to determine Kr and Pc for two-phase multicomponent transports, where these parameters also depend on component concentrations, i.e. kr(s,c) and pc(s,c).Two sister cores from the same outcrop are used for the SSTT and wettability measurement experiments. The SSTT is performed using a sequence of HS injection → core re-initialization → LS injection to enable comparison of Kr and Pc curves for the same initial conditions. The modelling resultsusing a well-posed inverse algorithm - indicate a significant decrease in relative permeability for water, an insignificant increase in relative permeability for oil, a slight reduction in residual oil saturation, and a negligible downward shift in the Pc curve after LS water injection. This is explained by the formation damage caused by the mobilization of fine particles and the consequent pore-scale flow diversion due to pore plugging.

Impact assessment of strain-dependent permeability on reservoir productivity in CSS

Geomechanical analysis is essential to assess the productivity forecast of cyclic steam simulation (CSS) operations in heavy oil reservoirs. The high-temperature and high-pressure fluid injection, as well as depletion in unconsolidated and poorly cemented porous media during CSS, may generate a relevant stress–strain response at levels that can lead to irreversible changes in reservoir permeability. Therefore, it is fundamental to consider permeability dependence on rock strain to properly analyze the impact of geomechanics, pressure, and temperature on reservoir performance. This paper implements a proposed directional strain-dependent permeability model to assess the productivity and compare it with a conventional volumetric permeability model through numerical simulation, considering the effects of wellbore creation on the stress–strain initial state. An explicit coupling between CMG-STARS and the geomechanics in-house simulator GSIM is carried out to perform the simulations using the proposed model. The results of oil production rates and permeability profiles show competitiveness between dilation and compaction periods that modify the structure of the porous media. There is a significant influence of stress state, strain, and injected energy on the permeability parameter. The approximations of this study might be used for feasibility assessment and optimization of CSS when integrating reservoir flow and geomechanical behavior analysis in productivity forecast.

A novel film based on gluten, pectin, and polyphenols and its potential application in high-fat food.

A novel film based on some natural ingredients (wheat gluten, pectin, and polyphenols) was used to improve the quality and storage stability of high-fat food due to their good sustainable, mechanical, and edible properties. With the addition of polyphenols from Cedrus deodara (in the form of pine-needle extract (PNE)), the physicochemical properties (thickness, moisture content, and color), mechanical properties (tensile strength and elongation), barrier properties (water vapor, oil, and oxygen permeability, transmittance), and thermal stability of the composite film were improved. According to the analysis of infrared spectroscopy and molecular docking, the main compounds of PNE interacted with wheat gluten by hydrogen bonds and hydrophobic forces to form a compact and stable structure. In addition, the composite film showed a remarkable antioxidant capability to scavenge free radicals, and the film matrix could effectively protect the antioxidant activity of PNE. Furthermore, using cured meat as a model, the composite film exhibited a fine packaging performance in high-fat food during storage, which could obviously inhibit the excessive oxidation of fat and protein of cured meat and was beneficial in forming its special flavor. Our results suggest that the composite film possessed good properties and had potential for packing of high-fat foods, which could improve the quality and safety of food during processing and storage. © 2023 Society of Chemical Industry.

Promising Energetic Melt-Castable Material with Balanced Properties.

As one of the most widely used energetic materials to date, trinitrotoluene (TNT) suffers from several generally known drawbacks such as high toxicity, oil permeability, and poor mechanical properties, which are driving researchers to explore new high-performance energetic melt-castable materials for replacing TNT. However, it still remains a great challenge to discover a promising TNT alternative due to the multidimensional requirements for practical applications. Herein, we reported a new promising energetic melt-castable molecule, 4-methoxy-1-methyl-3,5-dinitro-1H-pyrazole (named as DMDNP). Besides a reasonable melting point (Tm: 94.8 °C), good thermostability (Td: 293.2 °C), and excellent chemical compatibility, DMDNP exhibits some obvious advantages over TNT including more environmentally friendly synthesis, high yield, low toxicity, low volume shrinkage, low mechanical and electrostatic sensitivities, etc., demonstrating well-balanced properties and great promise as a TNT replacement.

Research and implementation of encoding and decoding technology of Layered Water Injection Based on Wave Code

The layered water injection technology based on wave code communication is one of the fourth-generation separated layer water injection technology, widely used in low permeability oil field with pressure operation injection Wells, has the advantages of simple operation and low cost. However, there is a problem of low communication efficiency. In order to solve the problem of low communication efficiency, this paper compares the advantages and disadvantages of amplitude time modulation encoding and pulse position interval encoding, and proposes a method based on pulse position interval encoding and decoding. Finally, the pressure wave communication experiment is carried out. The results show that when the pulse width is set to 5s, the communication time of a set of opening instructions is only 3 minutes, which greatly improves the communication efficiency of the wave coding process. The research on encoding and decoding can provide technical and theoretical support for improving the communication efficiency of layered water injection based on wave code.

Development scheme screening considering reservoir damage based on the AHP model

The development process of oil and gas fields is affected by engineering and geology. Reservoir damage is significant as a bridge connecting these two disciplines. The life cycle of oil and gas fields can be prolonged by making development plans that consider reservoir damage. Therefore, this study performed experiments and discusses a Cretaceous reservoir development in the Chun17 block of the Chunguang Oilfield. We have carried out five sensitivity experiments on typical cores from the block, and analyzed lithology, physical properties, and crude oil. A mathematical model based on the Analytic Hierarchy Process (AHP) was then established based on the core data.Overall, the reservoir in the study area has ultra-high porosity and high permeability. The reservoir has moderately strong water sensitivity (damage rate is 38 ~ 90%) and moderately strong alkali sensitivity (damage rate is 22 ~ 75%). The crude oil belongs to extra-heavy oil reservoirs (containing 2.43% wax, 0.96% sulfur, 20.25 m% gum, 7.35 m% asphalt, 38.26 m% saturated hydrocarbon, and 27.51 m%). The crude oil is sensitive to temperature changes. Based on the AHP model analysis, the development scheme chooses the third (weight 0.1757) of the conventional analytic results of AHP; the Thermal oil production C1 scheme has the most stable future trend and appears to be the best option. In the next step, using fire flooding technology to develop the reservoir will benefit the most economically. The workflow consisting of "conclusion of reservoir experiment → AHP mathematical modeling → verification of relative permeability of high-temperature oil and water → verification of trial production" is simple and effective. The findings of this study can help to better understand the idea and process of making development plans for sensitive oil and gas fields through reservoir evaluation. Combining experimental data with mathematical modeling can find a balanced combination point in qualitative and quantitative analysis. Whether this combination point is correct can be verified by field engineering practice.

Effect of Heterogeneity on Capillary Pressure and Relative Permeability Curves in Carbonate Reservoirs. A Case Study for Mishrif Formation in West Qurna/1 Oilfield, Iraq

The special core analysis tests were accomplished on a set of core plugs for Mishrif Formation (mA, mB1, and mB2cde/mC units) in West Qurna/1 oilfield, southern Iraq. Oil relative permeability (Kro) data and the Corey-type fit of the data as functions of the brine saturation at the core outlet face for individual samples in the water-oil imbibition process to estimate relative permeability measurements by the centrifuge method were utilized. Identical correlations for oil and water relative permeabilities were extracted by steady-state and unsteady-state methods. For the mA samples, the gas-water capillary pressure curves were within a narrow range (almost identical) indicating that mA is a homogeneous unit. Kro curves for three mB2ab plugs were practically identical, that is referring to the homogeneity in the upper portion of the unit. The mB2 unit has a more solid‐phase concentration than other units. In addition, the general trend of low residual oil saturation is related to the raising in porosity but no reliable correlation between the residual oil saturation to water drive (Sorw) and Klinkenberg-corrected permeability (Kinf). Based on the correlation between the effective oil permeability at the initial water saturation [ko(Swi)] and (Kinf/f)1/2 for the high-permeability lithofacies mB1 plugs, ko(Swi) is approximately equal to or exceeds Kinf. While ko(Swi) was below Kinf for the other samples. New good empirical equations were obtained for effective gas permeability at final water saturation versus Kinf, as well as, for Kro and Krw versus saturation for all lithofacies.

Key parameters and dominant EOR mechanism of CO2 miscible flooding applied in low-permeability oil reservoirs

CO2 miscible flooding is a prospective production method to enhance oil recovery (EOR), especially in low-permeability reservoirs. However, there is a lack of comprehensive and systematic understanding of the key parameters and dominant EOR mechanism of CO2 miscible flooding. In this work, the sensitivity of key parameters, such as oil viscosity, permeability, permeability ratio, and pressure, is analyzed by CO2 flooding physical simulation experiments. The adjuvants for CO2 miscible flooding of the Changqing crude oils are evaluated and optimized. The production performance of overpressure CO2 miscible flooding is studied by CO2 core flood test, and the oil micro-distribution before and after CO2 miscible flooding is characterized using nuclear magnetic resonance (NMR), and the micro EOR mechanism of CO2 miscible flooding is revealed. The results show that CO2 immiscible flooding is suitable for the development of low-viscosity crude oil (<50 mPa s), especially for oil viscosity of less than 10 mPa s. CO2 miscible flooding is advisable for low-permeability and medium and high-permeability reservoirs, especially for reservoir permeability of higher than 10 mD. Above the MMP, the oil recovery factor is over 85% and the increase rate slows down with pressure, CO2 miscible flooding is preferred for the high-pressure reservoir. CO2 miscible flooding is applicable for reservoirs with a permeability ratio of less than 2.5, especially for a permeability ratio of less than 2. Compared with 0.8 times MMP pure CO2 flooding, the time of gas channeling, and oil recovery for CO2 miscible flooding is delayed from 0.69 PV to 0.76 PV, and enhanced to 93.04% from 72.61%, respectively, with the help of adjuvants for CO2 miscible flooding, NP-9. The adjuvants for CO2 miscible flooding could effectively promote the realization of miscible flooding for CO2 and crude oils with an injection pressure of less than the MMP. CO2 has excellent oil displacement ability in low-permeability reservoirs, especially for miscible flooding, and the core oil saturation is obviously reduced. Overpressure CO2 miscible flooding could expand the swept volume and more efficiently displace oil in low-permeability reservoirs compared to an injection pressure of 1.0 times MMP. After overpressure CO2 miscible flooding, the residual oil in the low-permeability cores is distributed more evenly.

Paper packaging materials: modeling and optimization of hydrooleophobic composition

Introduction. A high level of barrier and protective properties, resistance to moisture penetration (water, steam) and air resistance are the main requirements for packaging paper for food products. Problem. Polyvinyl alcohol-based polymer coatings are widely used for packaging paper; however, such coatings tend to have poor water resistance due to the hydrophilic and water-soluble nature of polyvinyl alcohol. Polyamide-epichlorohydrin resins are used to provide mois­ture resistance of the paper, and glycerol is used for the elasticity of the coating. At the same time, the complex effect of these components in the mixture for surface treatment of paper on the quality of the products has not been sufficiently investigated. Methods. Compositions based on aqueous solutions of polyvinyl alcohol brand 7/18 of the highest grade, polyamideamineepichlorhydrin EKA WS 325 and glycerol brand PK-94 were used to obtain a moisture-resistant, waterproof and fat-proof packaging material. Polyacryla­mide in the amount of 0.25 wt. % was used as a func­tional additive, a viscosity regulator of the com­position, and water was used as a solvent. Model compositions with different ratios of the main components in accordance with the central com­posite rotatable plan of the experiment were app­lied to the tests according to the methods adopted in the pulp and paper industry. STAT-SENS software was used for mathematical processing of the experimental results. A multi-criteria opti­mization method was used to find the optimal range of parameters of the hydrooleophobic composition. Results. The 15 model compositions have been developed. The influencing factors were the content of the polyvinyl alcohol, polyami­deamineepichlorhydrin, glycerol. The quality indi­cators of the treated paper-base were selected as the response functions of mathematical models: oil permeability, air permeability, destructive force, moisture resistance, surface absorption. Conclusions. The developed composition is optimal and makes it possible not to exceed its consumption during application to fibrous mate­rial, in particular paper. The composition pene­trates the thickness of the paper to an optimal depth evenly over the entire surface of the paper, which makes it possible to provide the paper with uniform barrier properties, mechanical strength and wet-strength along the plane of the canvas. In addition, glycerol gives elasticity to the resulting coating and prevents it from cra­cking during repeated bending.

Superior enhancement of imbibition recovery by novel surfactant mixtures with a large hydrophobic group combined with nanosilica

AbstractLow interfacial tension (IFT) drainage and imbibition are effective methods for improving oil recovery from reservoirs that have low levels of oil or are tight (i.e., exhibit low oil permeability). It is critical to prepare a high efficient imbibition formula. In this work, a novel 2,4,6‐tris(1‐phenylethyl)phenoxy polyoxyethylene ether hydroxypropyl sodium sulfonate (TPHS) surfactant was synthesized and evaluated for imbibition. Its structure was confirmed by Fourier transform infrared spectroscopy and the interfacial tension (IFT) of the crude oil/0.07% TPHS solution was 0.276 mN/m. When 0.1 wt% TPHS was mixed with 0.2 wt% alpha olefin sulfonate (AOS), the IFT was lowered to 6 × 10−2 mN/m. The synergy between nanoparticles (NPs) and TPHS/AOS mixed surfactant was studied by IFT, contact angle on sandstone substrates, zeta potential, and spreading dynamics through microscopic methods. The results show that the surfactant likely adsorbs to the NP surface and that NP addition can help the surfactant desorb crude oil from the glass surface. With the addition of 0.05 wt% SiO2 NPs (SNPs), the imbibition oil recovery rate increased dramatically from 0.32%/h to 0.87%/h. The spontaneous imbibition recovery increased by 4.47% for original oil in place (OOIP). Compared to flooding by TPHS/AOS surfactant solutions, the oil recovery of forced imbibition in the sand‐pack increased by 12.7% OOIP, and the water breakthrough time was delayed by 0.13 pore volumes (PV) when 0.05% SNPs were added. This paper paves the way for enhanced oil recovery in low‐permeability sandstone reservoirs using novel TPHS/AOS surfactants and SNPs.

In-situ combustion technique for developing fractured low permeable oil shale: Experimental evidence for synthetic oil generation and successful propagation of combustion front

The idea of in-situ combustion (ISC) for oil shale development and conversion has been proposed recently. Due to the low permeability of oil shale, it usually requires fracturing operation before air injection. However, one of the biggest technical questions is, whether the combustion front can be established and steadily propagate in the low permeable oil shale with fractures. To date, no experimental work has been reported to support this. The target of this work is to provide experimental evidence to answer this question. We have managed to create a novel method for packing and fracturing oil shale core samples in a combustion tube for simulating ISC processes. A systematic analysis for the physical–chemical modeling of ISC process in combustion tube was performed, including temperature profile, pressure drop buildup, composition of produced gases, X-ray computed tomography (CT) and visual inspection, as well as total organic content analysis of oil shale samples before and after combustion, calculation of combustion parameters (air requirement, air/fuel ratio, apparent atomic H/C ratio, oxygen utilization, and O2/fuel ratio), and synthetic oil production. All results indicated the successful establishment and propagation of the combustion front in the fractured, low-permeability oil shale sample. In addition, the permeability of oil shale was increased 2–3 times during combustion, which can be an important factor that supports the stable propagation of the combustion front. Furthermore, the effect of water and catalysts on ISC performance was investigated. It was found that water promotes the cracking reactions of heavy oils to produce CO2 and hydrocarbon gases, and the co-existence of catalysts and water together further improved the performance of the ISC process and synthetic oil production. The findings in this work provide the experimental evidence of the successful establishment and propagation of combustion front in fractured, low-permeability oil shale, and technically proves the feasibility of using ISC technology for in-situ retorting of oil shale to generate synthetic oil for the development and conversion of low permeable oil shale with additional fracturing.

Permeability prediction of considering organic matter distribution based on deep learning

At present, researchers predict permeability through core experiments that require specific experimental conditions and methods, which are difficult and time-consuming. Conventional simulation methods for predicting permeability require considerable computational resources. Therefore, deep learning can be used as a pore-scale simulation prediction method. In this study, we established a workflow for directly predicting permeability from images. Considering that the mineral properties of the nanopore wall of shale oil have a large influence on the flow, a core dataset with organic distribution was constructed with random circles, and the slip influence of organic pores was considered. From our dataset, we found that the average permeability with organic distribution was 32.3% higher than that without organic distribution. Therefore, to simulate the microscopic flow and predict the permeability of shale oil, considering the differences in the pore flow mechanisms of different minerals is necessary. We designed a convolutional network for the dataset, adopted the structure of SE-ResNet, added the squeeze-and-excitation (SE) module to the double-layer residual module of ResNet18, and combined the characteristics of the SE block with the attention mechanism and ResNet to effectively obtain the information between channels and avoid the problem of gradient disappearance or explosion. Using SE-ResNet for directly predicting the apparent permeability from images, the accuracy of the test set reached 88.5%. The model had strong generalization ability, and the SE-ResNet could map the image of the core to the apparent permeability, which was approximately 100 times faster than the direct flow simulation.

A numerical simulation investigation on low permeability reservoirs air flooding: Oxidation reaction models and factors

A precise oxidation reaction model determines the reliability of numerical simulation results and the prediction of field performance of air injection-based enhanced oil recovery (EOR). By reviewing the classical oxidation reaction model and combining with geological characteristics of a low permeability reservoir, this work creatively divides pseudo-components and temperature regions and further proposes the improved low temperature oxidation (LTO), middle temperature oxidation (MTO), and high temperature oxidation (HTO) numerical models with chemical reaction coefficients. The EOR effects of reservoir temperature, permeability, air flow rate and bottom hole pressure during LTO and full temperature regions are determined on the basis of a 3D reservoir simulation model via CMG STARS. The results show that peak oil production rates of N2 flooding and LTO are 17.70 and 29.97 m3/d, respectively. The cumulative oil production in LTO stage is about 35%, which is higher than that in N2 flooding. The oxygen addition reaction in LTO stage can release much heat and increase sweep efficiency from thermal expansion and viscosity reduction. The peak oil production rates of LTO and full temperature oxidation (FTO) reactions are 42.16 and 44.34 m3/d, respectively, and the cumulative oil production of the FTO model was about 17% higher than that of LTO. The FTO model could more truly reflect the production performance during air flooding of low permeability oil reservoir. Strong oxygen consumption capacity and significant heat release effects can be observed under higher initial temperature, permeability, air flow rate, and lower bottom hole pressure. Thermal flooding and flue gas flooding are the main EOR mechanisms in FTO process. Considering the inescapable field problem of gas channeling, thorough contact between oil and air can be promoted by artificially preheating oil reservoir and adjusting air injection rate and pressure. Thus, oil recovery can be further improved under the premise of ensuring the safety of field application of air flooding technique.

Dynamics of the oil reservoir depletion

In order to study the dynamics of depletion in heterogeneous oil reservoirs on the base of combined finite-element-difference method for the non-stationary problem of piezoconductivity we have carried out a numerical simulation of the pressure distribution in vicinity of the operating well. At that we have taken into account the heterogeneous distribution of filtration characteristics inside the reservoir and the oil infiltration parameters on the boundaries of the reservoir. The developed method for solving the non-stationary problem of piezoconductivity in deformed oil formations allows us adequately to describe the distribution of pressure near production and injection well systems in real operating conditions. We have shown that depletion processes in vicinity of the active well mainly depend on the intensity of oil production and the degree of oil infiltration at the boundaries of the reservoir’s area and to a lesser extent on the filtration parameters inside the reservoir. Therefore, in order to maintain the proper level of oil production in the reservoir’s area, it is necessary, for example, thanks to the use of modern technologies (system of injection wells), to ensure a sufficient inflow of the oil phase at the borders of the considered area. We have shown that in the cases of low oil infiltration at the boundaries of the reservoir area, the value of depletion is directly proportional to the production power of the well. At the same time, a decreasing of the reservoir permeability leads to a slow downing of depletion processes. The limiting value of the oil boundary infiltration coefficient, which allows achieving industrial oil production, is m. At that, the time of reaching of the stationary productive regime is directly proportional to the value of the oil permeability coefficient inside the reservoir. Before installing a system of production and injection wells in heterogeneous oil reservoirs, it is necessary to carry out a systematic analysis of the degree of depletion of the working reservoir’s areas in order to place them in such a way that would ensure the effective dynamics of filtration processes around these areas.

Numerical study on the impact of water-rock interactions on the propagation of water-flooding induced fracture

Introcution: Water-flooding is an effective way to develop the extra-low permeability oil reservoirs and the water-flooding induced fracture (WIF) can improve waterflooding efficiency. However, geomechanical properties of rocks may alter due to the water-rock interactions, which usually increases the heterogeneity of reservoir properties and affects the WIF propagation.Methods: In this study, a method to calculate the WIF propagation length was proposed and numerical models were established considering the effect of water-rock interactions on geomechanical properties. In addition, the numerical model of stress distribution of the WIF propagation was validated by theoretical solutions based on the fracture mechanics. Moreover, the WIF propagation mechanism and the effect of water-rock interactions on the WIF propagation was analyzed.Results: Results indicate that the numerical model is valid to calculate the stress distribution induced by the WIF with an error under 5%. In addition, the WIF propagation can be affected by several factors, including the injection pressure, the damage variable and the initial fracture length. Noteworthy, the injection pressure should be strictly controlled because the WIF propagation is highly sensitive to the injection pressure. An increase of 2 MPa in the injection pressure can result in 90 m WIF propagation length, accounting for 64% of initial fracture length in the case studied in this work.Discussion: Moreover, water-rock interactions aggravate the heterogeneity of the reservoir and promote the WIF propagation due to the alteration of the geomechanical properties such as Young’s modulus. Therefore, the WIF can propagate even if the injection pressure is less than the minimum horizontal stress. Furthermore, the stress intensity factor (KIA) and WIF propagation length increase with the initial fracture length, which may lead to sudden water flux and reduce the efficiency of waterflooding.

Refracturing well selection method for ultra-low permeability reservoir based on multi-parameter coupling

At present, with the continuous increase in the development of ultra-low permeability reservoirs, fractures are prone to closure during the initial fracturing operation, which will affect the fracture conductivity to a certain extent, and the oil well production shows a gradual decline trend, and the water content of the target oil well is gradually increased. Therefore, in order to ensure a better recovery rate of ultra-low depth oil reservoir, it is necessary to use re-fracturing reconstruction technology for some low-production oil Wells, so as to gradually improve the conductivity of fractured fractures near the target oil well and restore the actual productivity of a single well, which is conducive to realizing the stable production of ultra-low permeability oil reservoir.

Understanding the Flow Mechanism of Fuyu oil layer in a certain Block

The Fuyu oil layer in a certain block is an ultra-low permeability oil layer. The development scale of sand bodies in the Fuyu oil layer is narrow, with rapid changes in facies on the plane, strong reservoir heterogeneity, and complex oil and gas accumulation and oil water distribution. Understanding the flow mechanism of the Fuyu oil layer in a certain block can help improve the development effect of this block