Low Permeability Oilfield Research Articles

Investigation on the preparation of nanoparticles by inverse micro-emulsion polymerization for enhanced oil recovery

Polyacrylamide nanoparticles attracted increasing interest as profile control agents in oilfield development owing to the characteristics of deformation and continuous expansion in core pore. In this article, the structure and morphology of polyacrylamide nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). And the fluorescence microscopy and core displacement equipment were used to evaluate the properties of the expansion and plugging properties. Results showed that the nanoparticles prepared by inverse emulsion polymerization can be able to pass through the pores in the rocks due to the uniform particle size which is less than 500 nm. When the nanoparticles were in contact with water for 72 hours, the average particle size increased to 12.2 μm. The water-swelled nanoparticles can effectively block the high-permeability layer and improve the oil recovery in the low-permeability layer. The results obtained in this paper reveal the mechanism of elastic deformation and expansion characteristics of polyacrylamide nanoparticles, and further prove the great potential of nanoparticles to enhance oil recovery in the development of low permeability oilfields.

Study on Clear Water Acidic Fracturing Increasing Injection Technology in Sandstone Oilfield

In view of the fact that it is difficult for some water injection wells in low permeability oilfields to absorb water and the general effect of conventional measures to increase injection, clean water acid fracturing technology research and field test of sandstone in low permeability reservoirs have been carried out. On the basis of fully investigating the adaptability of acid fracturing in sandstone reservoirs and combining with the actual development of low permeability oilfields in our factory, the technology of clear water fracturing and balanced acid fracturing is organically combined. After a lot of theoretical calculation, the construction parameters are optimized, and the suitable fracturing technology is optimized, which greatly reduces the requirements of surface construction equipment. At the same time, through indoor experiments, the suitable well entry fluids are screened to ensure the construction effect. At present, the technology has been tested in 6 wells and achieved good injection increase effect.

Composite Plugging Removal Technology and Application in Low Permeability Oilfield

In an oilfield factory, the blocking and jam in Chang 2 reservoir is very serious. In recentyears, according to analysizing different plugging mechanism and optimizing acidizing formula, theoptimal plugging removal technology was formed suitable for the solution for the Chang 2 reservoirof oilfield factory. This plugging removal formula increases the efficiency radius, and increases thedosage of additives to protect the pipe, rod and pump from the precipitation such as Ca2+and Mg2+,which causes new pollution. Reasonable multiple technologies were designed, and low displacementmethod was used in the injection process, aiming at the characteristics of Chang 2 reservoir. Thismethod extends the time of plugging removal fluid staying around the well bore, which can eliminateplugging near well bore area effectively, and improve the permeability. DQ-1 composite pluggingremoval and other kinds of plugging removal methods have been used more than 50 times, and theeffect is remarkable, which made a positive contribution to stable production of the oilfield.

Research on Intelligent Energy-saving Algorithm of Oil Pumping Based on BP Neural Network

In order to enhance the international competitiveness of China’s oilfields, this paper reduces the phenomenon of high energy consumption in low-permeability oilfields, reduce electricity costs, increase oil production, and improve oilfield efficiency. In this paper, an intelligent energy-saving algorithm based on BP neural network is proposed for continuous oil recovery. This algorithm analyzes the main influencing factors of oil production and collects sample data from two aspects of oil production and electricity consumption cost. The BP neural network model with single hidden layer is constructed. The number of hidden layer neurons is determined. The output of oil and the unit speed of oil pumping are predicted, and combined with the time-sharing electricity price to adjust the times of oil pumping unit time to reduce the cost of electricity. The experimental results show that the proposed intelligent pumping energy-saving algorithm effectively improves the pumping efficiency, can save the electricity cost to a certain extent, realizes the intelligent control of pumping unit, and makes the oil field achieve high production and efficiency.

CO2 Sequestration-EOR in a Tight Oil Reservoir: Estimation of Dynamic CO2 Storage Capacity Using a Two-Stage Well Test

Evaluation of an accurate CO2 dynamic storage capacity, ultimate recycled CO2 and enhanced oil recovery (EOR) are key factors for a successful CO2 EOR project. The Yanchang Petroleum Company (YP)’s low permeability oil field is located at Ordos Basin - China with a very short and inefficient primary and secondary oil recovery and, therefore, YP proposed CO2 EOR as a potential tertiary oil recovery approach. In this work, the Wuqi reservoir in the Yanchang field is selected to evaluate the feasibility of full-field CO2 sequestration-EOR. The Wuqi reservoir has been in production for over a decade with historical data that can be used for a history matching process. To acquire essential dynamic data for evaluation of the CO2 injectivity/dynamic storage capacity, a specific two-stage pilot well test is proposed to inject first water and then CO2. It will provide relatively accurate calculated permeability for water (test phase 1) and CO2 (test phase 2) at the injection well. Also, the test will qualitatively estimate the location of water and CO2 fronts in the reservoir over time. Using two monitoring wells simultaneously, significantly increases the radius of investigation (ROI) that can be achieved for a given injection scenario and will also describe directional heterogeneity in the reservoir. When informed by the pilot test data, the model can be used to estimate the CO2 injection rate, ultimate cumulative CO2 injection and oil production and CO2 injection well numbers over 15 years of CO2 sequestration-EOR, which can be utilised for further techno-economic analysis of the project.

Study on the response characteristics of oil wells after deep profile control in low permeability fractured reservoirs

AbstractThe rhombus inverted nine-spot well pattern is often adopted in low permeability oilfield development, which has the advantage of high oil production rate and flexible adjustment. Due to the strong heterogeneity of the low permeability reservoirs, the oil wells along the fracture direction are heavily water-flooded and the water cut rises quickly, and the oil wells on both sides of fractures have no response to water injection. Hence, deep profile control is an effective way to solve this kind of plane contradiction, and is widely applied in the low permeability oilfield development. However, because of the asymmetry of the rhombus inverted nine-spot well pattern and the heterogeneity of the low permeability reservoirs, there are differences in the response characteristics of oil wells at different locations after deep profile control. In this paper, combined with physical experiments and numerical simulations, we analyzed oil increment, the distribution of streamlines and slugs of wells at different locations before and after deep profile control, and evaluated the response characteristics of oil wells of rhombus inverted nine-spot well pattern after deep profile control in low permeability fractured reservoirs. It is concluded that the effect of increasing oil production of the side wells is better than that of the angle wells after deep profile control, and the response sequence is side well, angle well in short axis, and angle well in long axis, which is also verified by the practical results of deep profile control in Daqing Oilfield.

A fracture identification method for low-permeability sandstone based on R/S analysis and the finite difference method: A case study from the Chang 6 reservoir in Huaqing oilfield, Ordos Basin

Low-permeability reservoirs are characterized by poor physical properties, strong heterogeneity and natural fractures. Accurate identification of the fracture distribution is of great significance for the exploration and development of low-permeability reservoirs. Field outcrop, core and imaging log analyses show that stratabound vertical and high-angle structural fractures are the main types of fractures in the Chang 6 formation in the Huaqing oilfield. The fracture orientations include NE-SW, NNE-SSW, NW-SE, and NNW-SSE. The NE-SE-oriented fractures formed in the Himalayan stage, while the NW-SE fractures formed in the Yanshan period, and the other fractures derived from the fracturing in the Yanshan period during the Himalayan tectonic activity. The traditional rescaled range (R/S) analysis method is upgraded by introducing the finite difference (FD) method in this research, and the newly proposed method is called the R/S-FD method. Core data show that the R/S-FD method can accurately recognize vertical fractures and high-angle fractures. By comparing the fracture development section on the imaging log, it is found that fractures discrimination parameter F has a good linear relationship with both the fracture linear density and the fracture surface density. This method is verified by dynamic data (water injection profiles) and static data (image logging), and the results show that the recognition error is eliminated when the lower limit of F is 0.5, resulting in a crack identification accuracy of 76.9%. Combining the R/S and finite difference methods reduces the artificial recognition error of the traditional R/S method, and the recognition process is automated and intelligent. The R/S-FD method can be used in combination with multiple logging curves. A high fracture recognition accuracy could be accomplished by using this proposed method with only conventional logging curves, of great practical significance to some low-permeability oilfields that lack image logging data.

Study of Influences of Fracture Additives on Stability of Crude Oil Emulsion

Background: A hydraulic fracture is a key technology to increase production of the low permeability oil fields. Fracture additives such as gels, friction reducers, pH adjusters and clay stabilizers were injected into the underground. While more than 50% of the fracture fluid remains underground. The residue of fracture fluid comes out with the produced liquid (a mixture of crude oil and water) in the subsequent oil recovery process, which results in a highly stable crude oil-water emulsion. Objective: The stability and stable mechanism of the emulsion with fracture fluid have been experimentally investigated. Materials and Methods: The influences of fracture additives and components of crude oil on the stability of emulsion were investigated by bottle test and microscopic examination. The interfacial tension and modulus of dilation were explored by a spinning drop interfacial tension meter and an interface expansion rheometer, respectively. Results: The fracture additives played the key role on the emulsion stability. On one hand, the interface energy of oil-water was reduced by friction reducer (IFT was decreased from 24.0 mN/m to 1.9 mN/m), which was a favor for the formation of an emulsion. On the other hand, the dilational modulus of crude oil-water film was increased by hydroxypropyl guar and pH adjuster (Na2CO3) to form a viscoelastic film, which resulted in a highly stable emulsion. Conclusion: The residual fracture fluid accompanied by produced liquid resulted in a highly stable emulsion. The emulsion with fracture additives was difficult to be broken, which may affect the normal production of the oil field. A positive strategy such as developing demulsifier with high efficient should be put onto the schedule.

CO2 sequestration-EOR in Yanchang oilfield, China: Estimation of CO2 storage capacity using a two-stage well test

Depleted oil fields are often considered as the first target for carbon geo-sequestration. However, evaluation of an accurate CO2 dynamic storage capacity, ultimate recycled CO2 and enhanced oil recovery (EOR) are key elements for a successful project. The Yanchang Petroleum Company (YP)’s oil field is located at Ordos Basin and it is the second largest low permeability oil field in China with a very short and inefficient primary and secondary oil recovery. Thus, CO2 EOR was considered by YP to be an appropriate tertiary oil recovery approach. In this work, the Wuqi reservoir in the Yanchang field was selected to study the feasibility of full-field CO2 sequestration with EOR. The Wuqi reservoir has been in production for over a decade and has historical data that can be history matched. To acquire essential dynamic data for evaluation of CO2 injectivity/dynamic storage capacity, a specific two-stage well test design is proposed to inject first water and then CO2. It will provide accurate effective permeability estimates for water (test phase 1) and CO2 (test phase 2) at the injection well. The test will also inform the operator on the location water and CO2 fronts in the reservoir. Using two monitoring wells simultaneously, significantly increases the radius of investigation (ROI) that can be achieved for a given pumping scenario and will also describe the reservoir heterogeneity.

Experimental Study on Reservoir Sensitivity for Chang 6 Reservoir in CD Block of Ordos Basin

The development of low-porosity and low-permeability oil and gas fields has been concerned by scholars all over the world. This study focuses on the sensitivity study of Chang 6 reservoir in CD block of Ordos Basin. Through analysis by such technological means as rock core fluid flow experiment, X diffraction, rock core slices, scanning electron microscopy, it is proven that Chang 6 reservoir mainly gives primary to acid sensitivity, the velocity sensitivity is in the next place and the alkaline sensitivity and water sensitivity are in the end. The sensitivity minerals mainly cover the chlorite, calcite, ferrocalcite, dolomite, siderite and other minerals. Through discussion about the relationship among porosity, permeability and sensitivity indexes, it is deemed that he relationship among porosity, permeability and sensitivity indexes is closely related, and it is found through discussion for four kinds of sensitivity indexes that the trends of velocity sensitivity and acid sensitivity index curves are consistent, and the trends of alkali sensitivity and water sensitivity index curves are consistent. The consistency on relationship possibly enables that relationship between alkali sensitivity and water sensitivity are closely related to the fluid mineralization and the velocity sensitivity and acid sensitivity are closely related to the reaction rate of fluid.

Research on Property of Multicomponent Thickening Water Fracturing Fluid and Application in Low Permeability Oil Reservoirs

The clean fracturing fluid, thickening water, is a new technology product, which promotes the advantages of clean fracturing fluid to the greatest extent and makes up for the deficiency of clean fracturing fluid. And it is a supplement to the low permeability reservoir in fracturing research. In this paper, the study on property evaluation for the new multicomponent and recoverable thickening fracturing fluid system (2.2% octadecyl methyl dihydroxyethyl ammonium bromide (OHDAB) +1.4% dodecyl sulfonate sodium +1.8% potassium chloride and 1.6% organic acids) and guar gum fracturing fluid system (hydroxypropyl guar gum (HGG)) was done in these experiments. The proppant concentration (sand/liquid ratio) at static suspended sand is up to 30% when the apparent viscosity of thickening water is 60 mPa·s, which is equivalent to the sand-carrying capacity of guar gum at 120 mPa·s. When the dynamic sand ratio is 40%, the fracturing fluid is not layered, and the gel breaking property is excellent. Continuous shear at room temperature for 60 min showed almost no change in viscosity. The thickening fracturing fluid system has good temperature resistance performance in medium and low temperature formations. The fracture conductivity of thickening water is between 50.6 μm2·cm and 150.4 μm2·cm, and the fracture conductivity damage rate of thickening water is between 8.9% and 17.9%. The fracture conductivity conservation rate of thickening water is more than 80% closing up of fractures, which are superior to the guar gum fracturing fluid system. The new wells have been fractured by thickening water in A block of YC low permeability oil field. It shows that the new type thickening water fracturing system is suitable for A block and can be used in actual production. The actual production of A block shows that the damage of thickening fracturing fluid is low, and the long retention in reservoir will not cause great damage to reservoir.

Application of the new connotation of geology-engineering integration in low permeability oilfields:a case study on Xinli oilfield

Application of the new connotation of geology-engineering integration in low permeability oilfields:a case study on Xinli oilfield

Performance Evaluation and Application of the Surfactant Combinations showing Ultra-low Oil-Water Interfacial Tensions

Abstract In order to select a surfactant formulation with an ultra-low oil-water interfacial tension for application in a low permeability oil field, surfactant combinations were developed consisting of non-ionic alkanolamides, anionic alkyl benzene sulfonate and betaine in certain proportions. The results showed that the oil-water interfacial tension (oil from the Changing Jing'an field) could decease to 10−4 mN m−1∼10−5 mN m−1 in the wide surfactant concentration range of 0.3%∼0.6% and a salinity of 100 000 mg L−1 at 40°C∼70°C. From 2012 to 2013, the field tests of 8 injection and 39 production wells were carried out. The water-cut escalating rate decreased from + 1.26% to −0.15% monthly. The yield changing rate increased from −1.59% monthly to + 0.12%. The valid period of the test was more than 10 months. The improved oil recovery of the in-test well groups were predicted to increase 6.3% using type A characteristic curve of drive water. When comparing the three injection technologies, the key to the success of field application of surfactant combinations having an ultra-low oil-to-water interfacial tension is a consistent profile protocol of water injection.

Study of Corrosion Behavior of Oil Gathering Facilities with Co2 Flooding In Low-Permeability Oilfields

Carbon dioxide (CO2) gas flooding for enhancement of oil recovery is known to face challenges such as corrosion and scaling of oil-gathering facilities and environmental pollution. The corrosion behavior of the gathering facilities must be studied to select the optimum measures for protecting them from the corrosive effect of CO2. Surface corrosion of the separator, a key problem with using CO2, is evaluated in the present work. The corrosion characteristics, corrosion rate, and corrosion products in different functional areas of the facility were determined by the weight-loss method, scanning electron microscopy (SEM), and x-ray diffraction (XRD) analysis. The results indicate that pitting corrosion is the main characteristic of Fe-360 A steel facilities and that the average corrosion rate in vulnerable areas can reach 0.1358 mm/yr with formation of Fe2O3 and FeS. The combined effects of contact time and CO2 volume in conjunction with the activity of sulfate-reducing bacteria influence the corrosion kinetics and mechanism of Fe-360 A steel. The results are of great significance for minimizing corrosion using chemical inhibition and proper selection of materials that come into contact with CO2.

Research and Application of CO2 Flooding Enhanced Oil Recovery in Low Permeability Oilfield

This paper discusses the new progress and field application of CO2 flooding in low permeability reservoirs enhanced oil recovery. The study shows that CO2 flooding can improve the oil recovery rate of low permeability oilfield by more than 10%. The practice shows that the liquid CO2 injection in low permeability reservoir is easier than water injection, and the reservoir generally has better CO2 storage.

Mechanism of Fracture Generation in the Hole and Research on Optimization Design of Drilling Fracture Parameters

In order to increase the production of low permeability reservoir inclined or straight well, establish effective communication between the sand and improve development effect. For Daqing periphery low permeability oil field properties, such as large sandbody permeability difference, plane fast phase transition, narrow sandbody and scattered distribution. A straight and inclined well hydraulic fracture stimulation modification technology research and field application was launched. Studied the mechanism of crack generation in the hydraulic drilling hole and analyzed factors of crack situation in the hole of hydraulic drilling fracture, given parameter optimization method of hydraulic drilling fracturing, carried out hydraulic drilling fracturing on spot well selection test. The results show: At reservoir heterogeneity geo stress conditions, after the hydraulic drilling, the fracture cracks always rupture on contact surface of well and hole and then the crack extend along the direction of maximum horizontal stress. So reservoir heterogeneity is a necessary condition for generation of cracks in the hole. To make cracks in a certain position of hole after the hydraulic fracturing, reservoir heterogeneity must be a prerequisite, that there exists natural fractures in reservoir or geo stress heterogeneity. Pressure curve and fracture pressure curves intersect multiple cases. In these cases there will be many perforations along the crack. Considering the stress orientation, petrophysical, sedimentary facies, hole geometry parameters, the overall design system of hydraulic drilling fracturing parameters optimization is given. On spot selected well got a good effect. Liquid production increased to 4.8 from 1.7 tons. Oil production increased to 4.2 from 0.9 tons.

The Numerical Simulation Research of The Remaining Oil Distribution Regulation in Test Site of Low Permeability Oil Field

The Numerical Simulation Research of The Remaining Oil Distribution Regulation in Test Site of Low Permeability Oil Field

A mathematical model and numerical simulation of waterflood induced dynamic fractures of low permeability reservoirs

Based on abundant data of low permeability oilfields, dynamic fractures were conceptualized and their evolution, including cracking, extending and closing, were analyzed. A new model that describes the dynamic changes of fracture shape and properties was established and a software module was developed. The simulation results show that dynamic fractures cracked once the injection pressure was higher than the formation fracture pressure, and then extended continually, which showed a periodic variation relationship with the formation pressure and the injection volume. After the moderate injection, dynamic fractures remained the open status in a relatively long time, but then the whole fractures tended to close quickly, and these phenomena indicate that the dynamic fractures were significantly affected by the production condition. The presence of dynamic fractures provides a channel for the injection water. With the gradual extension of dynamic fractures, the injection water forms a narrow range of displacement, which leads to the severe imbalance of water flooding, aggravates the heterogeneity of low permeability reservoirs, and significantly affects the water cut rising rules of wells in all directions. However, dynamic fractures also show a positive effect on the establishment of an effective displacement system between the injection wells and the production wells.

The residual oil distribution regularity of low permeability oilfield

Abstract Study on the residual oil distribution regularity is the important thing during the middle and later stage of the oilfield. With understanding and development of oilfield, the research methods of remaining oil are varied. Well block A is a low permeability oilfield and complex relationship between injection wells and production wells. The well pattern has low control of sand body. Based on the characteristics and the geological and dynamic data, technology of integrated 3-D geological modeling with reservoir numerical simulation is ensured to study the residual oil. Finally, deposition facies and flowing units are studied to analyze the residual oil distribution regularity. As a result, the types of residual oil were confirmed and the basis for the following development adjustment of the well block is provided.

Water Drive Characteristic Curve Theory of Low Permeability Reservoir

The so-called water flooding characteristic curve refers to the oilfield water injection (or natural water drive) development process, a relationship between curve cumulative oil production, cumulative water production and accumulation of fluid production. These curves have been widely used for water injection development of dynamic and recoverable reserves forecast. After many years of practical application, summed up the four kinds of water drive characteristic curve, they have a good practical significance. Recoverable reserves are important indicators of field development and also the main basis for planning and design, while the application of water flooding characteristic curve can be predicted oil recoverable reserves. Four kinds of water flooding characteristics discussed above curve are mainly applied in high-permeability oil field, which did not consider starting pressure. In fact we should consider the impact of low permeability oilfield actuating pressure gradient on the water content. Here, we deduce the formulation considering the actuating pressure. Key words: Low permeability; Water flooding; Actuating pressure