Modeling of the effect of oil viscosity on cyclic flooding of oil reservoirs

The method of cyclic waterflooding is one of the most cost-effective methods of enhanced oil recovery. Simulation of cyclic waterflooding will take much more time than conventional waterflooding. This is due to the time step limitation which should be much less than the half-period of fluctuations and the characteristictime of pressures equalization in neighboring interlayers. This paper proposes the flow equations averaged over the cycle period in the case of a periodic law of variation in production rates or bottomhole pressures in wells that are free from the specified time step limitation and allow to simulate cyclic waterflooding in a time comparable to the time of simulating a conventional waterflooding. The simulations based on the averaged and conventional (used in flow simulators) equations of a two-phase flow are compared using a synthetic example and actual field areas in Western Siberia and Kazakhstan. A complete solution to the cyclic waterflooding problem involves the selection of the promising areas, well locations, as well as the period and duration of stimulation. As a rule, this requires running multiple simulations. Therefore, in order to reduce the number of simulation runs, in this paper we propose an efficient technology for 3D modeling of cyclic waterflooding in oil fields. This technology allows to select, in real time, the promising areas and to assess the effect on incremental oil recovery of such factors as locations of wells, the frequency of cycles, etc. Also, it allows to predict incremental oil production in a time much shorter than using a conventional simulator, without accuracy losses. The successful results of technology application in some fields of Western Siberia and Kazakhstan are given below.

Study of cyclic waterflooding for improving oil recovery in Lukeqin heavy oil reservoir

With low salinity waterflooding already implemented, cyclic waterflooding is under extensive research for increased oil recovery than conventional waterflooding. Low salinity cyclic water injection (CWI) is an interesting combination that offers the effects of both, with notably high oil recovery and less usage of water. Careful evaluation might promote the application of cyclic injection in the fields, especially on Alaska North Slope (ANS). Two phase flow experiments were conducted on representative sandstone cores. After establishing initial water saturation, Amott-Harvey Wettability tests were performed with spontaneous and forced displacement of the fluids by one another. Cyclic water floods were conducted to calculate oil recovery from the volume of produced fluids. Pulsed cyclic floods were programmed in the injection pump. The experiments were repeated with cores of different permeability and lab reconstituted brines of 22000, 11000 and 5500 ppm salinity. Results were compared with available data from continuous injection performed on the same cores. Cyclic floods were also tested for two symmetric on-off time intervals. With the dead oil experiments, it is observed that residual oil saturation (Sor) is achieved as early as 3-4 pore volumes (PV) of injected water in cyclic injection as compared to 6-7 PV’s in continuous injection. Additional oil recovery is observed in cyclic injection’s idle time, when the already flooded water spreads smoothly within the pores to displace oil out of the core. Better recovery was obtained with lower salinity brines. Within cyclic injection, shorter pulse intervals yielded better results. To conclude, low salinity CWI with shorter pulse intervals yield better oil recovery and early Sor. This is an attractive option for ANS operators.

The cyclic injection improves water-flooding sweep efficiency in heterogeneous reservoirs. The IOR-method was applied in many fields in Russia, USA, China. Cyclic injection potential to improve water-flooding efficiency was clearly demonstrated in a number of projects. The uncertainty which exists with the cyclic water-flooding is related to understanding the IOR mechanism, ability to accurately model and predict efficiency of the process, design a field application. In this work we discuss and evaluate parameters that affect cyclic water-flooding. The algorithms and analytical tool were developed to model cyclic injection and fluid cross-flow between stratified reservoir layers. The model accounts for compressibility effects, gravity and capillarity forces. The screening results of cyclic injection in the North Sea heterogeneous sandstone reservoir are presented. A wide-range sensitivity analysis was performed to estimate the process efficiency. The analysis with respect to rock-fluid parameters, heterogeneity, cycle length and pressure conditions allowed to rank the critical factors by their influence and importance for achieving efficient cyclic process. Cyclic injection has significant IOR potential in stratified sandstone reservoirs with high permeability contrast. The method can improve water-flooding sweep, accelerate oil production and increase oil recovery by up to 11%.

The paper summarizes the methods and effects of cyclic waterflooding in the southern oilfields of the Daqing Placanticline, discusses the feasibility and necessity of this process in lower permeability reservoirs, and analyzes systematically the main factors which impact the results of cyclic flooding. Production performance is compared and contrasted for fields developed by both conventional, and cyclic waterflooding. Based on field case histories, the impact of cyclic waterflooding on performance at different water cuts is evaluated. It is demonstrated that cyclic flooding should be implemented at low water cuts, but is beneficial at all development stages. Cyclic waterflooding is an effective measure to enlarge sweep volume and enhance conformance efficiency and oil recovery. The practices described can provide guidance for cyclic waterflooding in similar oilfields.

South Kazakhstan is one of the hydrocarbon rich provinces in Kazakhstan, which is among the top 20 oil producing nations. However, most of the big fields of the basin are entering the last stages of development. Consequently, operators look for opportunities to maintain economical production by applying IOR methods at lower costs. Hence, cyclic waterflooding was considered a good candidate because of no expenditures. The paper demonstrates the main stages, mechanisms, and results of the project. The schematic of cyclic waterflooding is carried out by changing injection rates in phases. This leads to fluid flows redistribution in heterogeneous reservoirs due to capillary forces. So, the field trial was implemented on the KK field, which is represented by stratified sandstone mostly waterflooded. The injection pattern is irregular and eight patterns participated in the project. Rates varied from 50 t/d up to 300 t/d. Phases consisted of one group of injectors introducing water at lower and another group at higher rates with one-month duration. After that, the wells’ rates were adjusted. Cyclic waterflooding has been in operation for almost a year. During that period, producers’ working modes haven't been changed. As the result of observations, some wells have moderate or even no impact, but some wells exhibited remarkable improvements, e.g. a producer which has three injection wells around experienced watercut decrease from 90% up to 40%, while oil rate increase from 1 t/d up to 5 t/d. Overall, oil production from a group of nearby producers whose oil rates were previously reducing with a 41% decline has a clear trend of full stabilization. The main aspect causing this phenomenon is watercut decrease. The parameter fell from 95% to nearly 86%. Thus, it became beneficial not only in terms of oil production but also surface infrastructure. Less water volume treatment is required and it is critical for gathering system under conditions of growing water production. Summing up all the above-mentioned cyclic waterflooding has big success in our field case study. The initial modest forecast turned to significant oil increment and watercut decrease. Moreover, the company saved money which makes this IOR approach the most preferable to implement. Therefore, additional two projects recently started on other similar fields. It is obvious that if properly managed, improved oil recovery is possible at no cost breathing new life into old fields.

There are some problems of high saturation sandstone reservoir in late development stage, such as low reservoir pressure level, low oil production volume and high water content ratio. At present, the conventional treatment measures are poor to improve the reservoir development efficiency. Through extensive investigation and comprehensive analysis, the cyclic water flooding method can effectively improve the reservoir development efficiency. This study is based on the theory of cyclic water flooding method to replace remaining oil. The numerical simulation of cyclic water flooding is carried out by establishing geological model of actual blocks. By analysing the influence of injection-production ratio, injection-production method and liquid production volume on the cyclic water flooding development efficiency, the cyclic water flooding scheme of high saturation sandstone reservoir in the late development stage is optimized.

Over the past decade, oil production in Western Siberia has declined by 10%, while the water cut–the proportion of water in the total fluid produced – has increased.At the same time, the average oil recovery factor remains relatively low at 38%. This situation emphasises the urgency of finding and studying cheap and effective methods to enhance oil recovery. This study analyses a two-dimensional filtration, two-phase flow model of a dual-layer reservoir, considering two scenarios: (A) the low-permeability layer located above the high-permeability layer, and (B) the low-permeability layer situated below the high-permeability layer. The main aim of this paper is study how body forces influence the oil saturation structure in a dual-layer reservoir during cyclic waterflooding. A second aim is to determine how the gain in oil production depends on the phase density difference (Δρ) using cyclic waterflooding method. Using numerical simulation, the authors performed a series of calculations by varying the density difference between oil and water for both reservoir configurations. The results show that Δρ has a significant impact on structure of oil saturation and on the duration of deposit development. As Δρ increases, the effectiveness of cyclic waterflooding decreases.

Cyclic injection is a process that improves waterflooding efficiency in heterogeneous reservoirs. The concept of cyclic injection is based on (1) pulsed injection and (2) alternating waterflood patterns. Cyclic injection has been successfully applied in a number of sandstone and carbonate oil fields in Russia. In the rest of the world, pulsed injection has had limited application, and only in naturally fractured reservoirs. Although changing the waterflood patterns is a common approach to deal with increasing water cuts, a more systematic approach with both pulsed injection and alternating flow directions is not. Cyclic injection has the greatest potential for improved recovery in heterogeneous, high-permeability-contrast sandstones and in naturally fractured carbonates and dolomites. The efficiency of the process is high in preferentially water-wet rocks saturated with compressible fluids. Capillary pressures and relative permeability effects are responsible for the improved cyclic oil displacement at the micro level. Improved sweep of the less permeable layers in communication with more permeable thief zones, better horizontal sweep achieved by changing waterflood patterns, and alternating the dominance between gravity and viscous forces are the key effects of cyclic injection on the macro level. The potential of cyclic injection at the Lower Tilje/Åre formations of the Heidrun Field in the Norwegian Sea has been evaluated. Some of the reservoir levels are highly heterogeneous, with large permeability contrasts vertically and horizontally. The current drainage strategy for these formations is water injection, with gas lift in producers when needed. Cyclic injection will improve waterflooding efficiency at virtually zero additional cost. Improved sweep, accelerated oil production, and reduced water cut are the main positive effects expected from cyclic waterflooding. The reserves are predicted to increase by 5 to 6% from the targeted reservoirs at Heidrun after 10 years of cyclic waterflooding.

When fractured low-permeability reservoirs enter a high water cut period, injected water always flows along fractures, water cut speeds increase rapidly, and oil production decreases quickly in oil wells. It is difficult to further improve the oil recovery of such fractured low-permeability reservoirs. In this paper, based on the advantages of in-depth profile control and cyclic water injection, the feasibility of combining deep profile control with cyclic water injection to improve oil recovery in fractured low-permeability reservoirs during the high water cut stage was studied, and the mechanisms of in-depth profile control and cyclic waterflooding were investigated. According to the characteristics of reservoirs in Zone X, as well as the fracture features and evolution mechanisms of the well network, an outcrop plate fractured core model that considers fracture direction was developed, and core displacement experiments were carried out by using the HPAM/Cr3+ gel in-depth profile control system. The enhanced oil recovery of waterflooding, cyclic water injection, and in-depth profile control, as well as a combination of in-depth profile control and cyclic water injection, was investigated. Moreover, variations in the water cut degree, reserve recovery percentage, injection pressure, fracture and matrix pressure, and water saturation were monitored. On this basis, the mechanism of enhanced oil recovery based on the combined utilization of in-depth profile control and cyclic waterflooding methods was analyzed. The results show that in-depth profile control and cyclic water injection can be synchronized to further increase oil recovery. The recovery ratio under the combination of in-depth profile control and cyclic water injection was 1.9% higher than that under the in-depth profile control and 5.6% higher than that under cyclic water injection. The combination of in-depth profile control and cyclic water injection can increase the reservoir pressure; therefore, the fluctuation of pressure between the matrix and its fractures increases, more crude oil flows into the fracture, and the oil production increases.

In order to develop methods to further enhance oil recovery after water flooding in low permeability reservoirs by improving oil displacement efficiency, the displacement mechanism of residual oil was studied by the application of different pertinent measures. For in-depth investigation of oil displacement and variations in residual oil saturation, a large number of visual glass model displacement experiments were performed with different methods, such as changing the displacement direction, cyclic water flooding, displacement pressure difference variation and polymer flooding. In this paper, the models were divided into three (low, medium and high) permeability levels, and the residual oil after water flooding was categorized in five different types: cluster, oil film, oil drop, columnar and blind end residual oil. The experimental results showed that cluster residual oil accounted for the largest proportion after water flooding. In addition, with the increase in model permeability, cluster residual oil saturation increased and other types of residual oil saturations decreased. Compared to other methods, polymer flooding showed maximum displacement efficiency for the same displacement pressure and permeability model. The procedure was then followed by changing the displacement direction, cyclic water flooding and changing the displacement pressure difference. The different residual oil types can be activated by different methods, for example, cluster and columnar residual oil by changing the displacement direction, cluster and columnar residual oil by cyclic water flooding, cluster and oil drop residual oil by increasing displacement pressure difference. Moreover, all of the above mentioned five (05) types of residual oil can be activated by polymer flooding.

Distinguished Author Series articles are general, descriptivere presentations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Introduction Until the U.S. Congress passed the Safe Drinking Water Act (PL 93–523)in Dec. 1974, regulation of subsurface injection wells was the sole province of the individual states. The Safe Drinking Water Act placed permitting of subsurface injection wells under the control of the Environmental Protection Agency (EPA). However, states were Protection Agency (EPA). However, states were encouraged to adopt or modify their underground injection-control(UIC)regulatory programs to obtain EPA approval, thereby returning authority to the states to administer the UIC program. This return is known as"primacy." During the 1940's and early 1950's, oil-producing states on their own initiative adopted effective regulations for subsurface disposal and injection wells used in oil and gas operations. Among other objectives, state injection-well rules were designed to protect freshwater aquifers. Legislative History History gives convincing evidence that state regulations were effective in protecting underground waters. Documented cases of pollution of fresh water aquifers by oilfield injection and disposal wells are few and limited in area. Congressional recognition of the effectiveness of state control programs wasevident in the original language of the Safe Drinking Water Act. However, Congress expressed its recognition more clearly in the Dec. 1980 amendments to the act (PL 96–502) by instructing the EPA to grant approval to existing state regulatory programs for oil and gas field injection wells programs for oil and gas field injection wells under general-standards rather than the more specific standards imposed on other classes of injection wells. Part C of PL 93–523 setsout the requirements for approvable state programs. Originally, states were required to comply with Sec. 1422 (b)(1)(A). Among other conditions, this section provided that a state program must meet all requirements of EPA regulations in effect under Sec. 1421. The Dec. 1980 amendments to the Safe Drinking Water Act added Sec. 1425, which allowed states greater flexibility in obtaining EPA approval for their existing Class II injection-well program. Sec.1425 gave states the option to demonstrate that their UIC program for Class IIwells generally meets the requirements of Sec. 1421 (b)(1), Subparagraphs (A)through (D), in lieu of the showing required under Sec. 1422 (b)(1)(A). Congress did include the provision in PL 93–523 that regulations and guidelinesadopted by the EPA and the states should not interfere needlessly with oil and gas operations (Sec. 1422[c]). The Senate committee report accompanying the actcomments further on this precaution as follows. …This Amendment prohibits regulations for state underground injection-control programs from prescribing requirements which would interfere with oil or natural gas or disposal of by products associated with such production, except that such requirements are authorized to be prescribed if essential to assure that underground sources of drinking water will not be endangered by such activity. …The Committee'sintent in adopting this amendment was not to require an impossible burden of proof on the states as a condition of promulgation of any such regulations. Rather, the Committee sought to assure that constraints on energy production activities would be kept as limited in scope as possible while still assuring the safety of present and potential sources of drinking water. present and potential sources of drinking water. Similar provisions were adopted with respect to EPA regulations. JPT p. 1409

Affected by the surrounding injection and production wells, the formation near the infill adjustment well is in an abnormal pressure state, and drilling and completion operations are prone to complex situations and accidents such as leakage and overflow. The conventional shut-in method is to close all water injection wells around the adjustment well to ensure the safety of the operation, but at the same time reduce the oil field production. This paper proposes a design method for shut-in of water injection wells around adjustment wells based on injection-production data mining. This method uses water injection index and liquid productivity index as target parameters to analyze the correlation between injection and production wells. Select water injection wells with a high correlation and combine other parameters such as wellhead pressure and pressure recovery speed to design accurate adjustment schemes. Low-correlation wells do not take shut-in measures. This method was applied to 20 infill adjustment wells in the Penglai Oilfield. The correlation between injection and production wells was calculated using the data more than 500 injection wells and production wells. After a single adjustment well is drilled, the surrounding injection wells can increase the water injection volume by more than 5000 m3. This method achieves accurate adjustment for water injection wells that are high correlated with the adjustment well. Under the premise of ensuring the safety of drilling operations, the impact of drilling and completion on oilfield development is minimized, and oilfield production efficiency is improved. It has good application and promotion value.

Affected by the surrounding injection and production wells, the formation near the infill adjustment well is in an abnormal pressure state, and drilling and completion operations are prone to complex situations and accidents such as leakage and overflow. The conventional shut down method is to close all water injection wells within 500 meters from the adjustment well to ensure the safety of the operation, but at the same time reduce the oil field production. This paper proposes a design method for shut-in of water injection wells around adjustment wells based on injection-production data mining. This method is based on the influence of correlation of complex pressure wells under injection and production conditions, and uses water injection index and fluid production index as research objects. Data mining methods are used to find highly correlated wells for precise adjustment instead of conventional adjustment. This method was applied to 20 infill adjustment wells in the Penglai Oilfield in Bohai Sea. The correlation between injection and production wells was calculated using the water injection index and fluid production index of more than 500 injection wells and production wells. Controlling the precise shut-in of highly correlated wells ensures that well pressures are kept within safe limits during drilling and completion operations and that no abnormalities occur. Low-relevant wells do not take shut-in adjustment measures. After a single adjustment well is drilled, the surrounding injection wells can increase the water injection volume by more than 5000m3. This method achieves accurate shut-in for water injection wells that are highly correlated with the adjustment well. Under the premise of ensuring the safety of drilling operations, the impact of adjusting drilling and completion on oilfield development is minimized, and oilfield production efficiency is improved. It has good application and promotion value.

Water flooding is one of the most important methods used in enhanced production; it was a pioneer method in use, but the development of technology within the oil industry, takes this subject toward another form in the oil production and application in oil fields with all types of oils and oil reservoirs. Now days most of the injection wells directed from the vertical to re-entry of full horizontal wells in order to get full of horizontal wells advantages.This paper describes the potential benefits for using of re-entry horizontal injection wells as well as combination of re –entry horizontal injection and production wells. Al Qurainat productive sector was selected for study, which is one of the four main productive sectors of South Rumaila oil field. A simulation model – named as SRFQ was used in the present work to predict the re-entry horizontal wells performance.Four scenarios were suggested to cover the full scope of the study; those scenarios are different in manner of wells combinations. Cumulative oil production, ultimate recovery percentage are two criteria were used to predict the performance and comparison of scenarios.Results from simulation model (SRFQ) runs revealed that the productive sector can be continue to gain 1564.331 MMSTB till 2020, without changing to any existing injection and production wells status, which is called the base scenario. While scenario no.1 needs some of work over and remedies jobs, which gives more cumulative oil production reaches to 1698.481 MMSTB till 2020.On another side, scenarios no. 2 and 4 are the most important scenarios because re-entry horizontal injection wells were implemented. Very good and encourage results were gained over the bas scenario from the sector under study.At last, scenario no.3 was suggested just to predict the production capacity of the Al Qurainat sector with re-entry horizontal production wells and existing vertical injection and production wells, while the cumulative oil production reaches 3398.481MMSTB.