Bottom Water Reservoir Research Articles

Distribution of flow characteristics and productivity evaluation of herringbone wells in bottom water reservoirs

Abstract With the characteristics of large drainage area and low drilling cost, the herringbone wells have become an important way to increase the well production, delay the coning and ridge of bottom water and improve the development effect. Due to the complexity of the herringbone wells flow characteristics, results that exists certain gap between the current production prediction and the actual production, so it is of great significance to study the flow and productivity of herringbone wells. In this paper, taking bottom-water reservoir as the research object, considering the interference between branch wellbore and perforations, analysis the flow characteristics and the productivity sensitivity factors of herringbone wells. The results show that the transient flow time in the reservoir is short, the closer to the wellbore, the greater the pressure changes. With the increases of the branches number, branches length and branch angle, the per unit length of the wellbore radial inflow decreases, and the decrease slows down after exceeding 3 branches. In the high anisotropy reservoirs, the phase angle has greater impact on the productivity of the herringbone well when the perforation density is low, at 180°, phase angle is best; when the perforation density exceeds 16 shots/m, the increase of productivity degree decreases. This study provides important guiding significance for the actual application in oil fields to optimizing the herringbone wells shape, rational production allocation, specifying reasonable work systems and enhance oil recovery in the bottom water reservoirs.

The Current Status and Development Trend of Water Control Technology for Horizontal Wells

In the advancement of bottom water reservoir development, water breakthrough poses a significant challenge to the productivity of oil and gas wells, underscoring the paramount importance of effective water control strategies. Given the intricate nature of the factors leading to reservoir water breakthrough, a one-size-fits-all approach to water management is non-existent. Rather, tailored water control techniques are necessary to address the diverse causes of this phenomenon. This paper delves into the evolution and application of water control technologies, particularly focusing on the prevalent horizontal well water control methodologies. Horizontal well variable density water control, segmented water control, double horizontal well oil recovery water control, along with advanced solutions such as ICD (Inflow Control Device), ICV (Inflow Control Valve), AICD (Autonomous Inflow Control Device), and AICV (Autonomous Inflow Control Valve) water control systems are comprehensively introduced. Furthermore, center-controlled, mechanical plugging, and chemical plugging water control technologies are also examined in depth, accompanied by a thorough analysis of their respective strengths, limitations, and adaptability to various scenarios. By keeping abreast of both domestic and international trends in horizontal well water control, the future trajectory of this field is forecasted. Emerging as key technologies are novel composite water control systems, dual-purpose water control and sand prevention techniques, and intelligent water control solutions. These advancements promise to revolutionize the management of water breakthrough in bottom water reservoirs, enhancing oil and gas recovery efficiency and sustainability.

Research and Practice on Implementing Segmented Production Technology of Horizontal Well during Extra-High Water Cut Stage with Bottom Water Reservoir

Bohai X oilfield has reached the extra-high water cut stage of more than 95%, dominated by the bottom water reservoir. The oilfield mainly adopts horizontal-well exploitation, with the characteristics of high difficulty and low success rate for well water plugging. To solve the above problem, the segmented production technology of horizontal wells was developed to guide oilfield applications and tap their potential. In the segmented design stage, the horizontal section is objectively segmented by drilling condition analysis, optimally based on drilling through interlayers or permeability discrepancy formation, simultaneously combined with the numerical simulation method. When implementing measures, annulus chemical packer materials are squeezed between segments to effectively inhibit the fluid flow between the open hole and the sand-packing screen pipe. Moreover, the packers are used to seal between segments to effectively restrain the flow between the screen and the central tube, achieving the establishment of compartments. In the production process, the valve switch on the central tube can be independently controlled by a remotely adjustable method to achieve optimal production. This segmented production technology was successfully tested for the first time in Bohai oilfield. Up to now, a total of six compartment measures have been implemented, remarkably decreasing water cut and increasing oil production for horizontal wells in the bottom water reservoir. This method does not require water testing, and the optimal production section can be chosen through segmented independent production, greatly improving the success rate of water-plugging measures for horizontal wells. This technology opens up a new mode for the efficient development of horizontal wells in bottom water reservoirs and is planned to be widely promoted and applied in similar oilfields.

Dynamics of Water Sighting and Injection Mechanisms in Fishbone Branch Wells in Bottom Water Reservoirs

Abstract Herringbone wells are effective in improving productivity for bottom water reservoirs; however, the main problem faced in the exploitation of bottom water reservoir is the ridge and cone of bottom water during the process of waterflooding, which leads to the decline of oil production. Therefore, predicting the breakthrough time and location of herringbone wells in bottom water reservoirs and then adjusting the water injection measures are of great significance for improving production and development. In this paper, we establish a three-dimensional coning model of bottom water to study the dynamic performance of bottom water rise, and the sequence of breakthrough position is determined by studying the breakthrough time along the wellbore. Based on the reservoir numerical simulation, we carry out a comprehensive adjustment of the water injection mechanism and develop a water injection scheme under the combination arrangement of vertical wells and herringbone wells. The results show that the bottom water breakthrough position of the branch well is mainly near the heel of the main branch or near the middle subsidence, and the recovery rate is the highest when the branch angle is 45 deg. The longer the shut-in time, the higher the recovery. The study is of great significance to optimize the layout and spatial structure, determine a reasonable working system, delay water channeling, and increase the cumulative production of herringbone wells.

Study on Visualization Water Drive Experiment and Mechanism in Bottom Water Reservoir Affected by Seepage Barrier

Study on Visualization Water Drive Experiment and Mechanism in Bottom Water Reservoir Affected by Seepage Barrier

A productivity equation of horizontal wells in the bottom water drive reservoir with an interlayer

The interlayer can effectively prevent the ridge of bottom water and has a non-negligible influence on the flow dynamics of oil and gas in the reservoir. In view of the above problems, this paper studies the influence of a bottom water reservoir with an interlayer on the critical productivity of horizontal wells and establishes a coupling model of seepage and wellbore flow in a bottom water reservoir with an interlayer. The critical productivity of horizontal wells in a bottom water reservoir with an interlayer can be evaluated more accurately. Firstly, the three-dimensional seepage field is approximately decomposed into internal and external seepage fields, and the critical productivity formulas of internal and external seepage fields are solved, respectively. Using the equivalent seepage resistance, the critical productivity formula of horizontal wells in interlayer bottom water reservoirs is obtained. The results are compared with the calculation results of the traditional productivity formula and the simulation results of the commercial software ECLIPSE. Second, based on the mass conservation principle and momentum conservation principle, the wellbore-reservoir coupling mathematical model of a horizontal well is established by the discrete method. Finally, the sensitivity analysis of the selected parameters is discussed in detail. The results show that: (1) compared with the traditional productivity algorithm, the algorithm considers the influence of interlayers on productivity and gives a detailed theory, a specific calculation process, and the importance of accurate prediction of wellbore flow. (2) The model is calculated by an example, and the calculation results are compared with the traditional formula and the commercial simulator ECLIPSE. The results show that the horizontal well productivity formula considering the influence of interlayer is closer to the simulation results of commercial software ECLIPSE, and the relative error is 8.56%. (3) The established coupling model considers the influence of interlayer radius length and horizontal well length. The general trend is that productivity gradually increases with an increase in interlayer radius length or horizontal well length, but the growth rate gradually decreases.

Laboratory Evaluation on the Water Flooding Characteristics in Bottom Water Reservoir Containing Interbeds.

Sandstone reservoirs with bottom water drive are widely distributed all over the world, which are characterized by the complex process of oil and water storage and transmission. At present, the research on the water flooding process and oil-water evolution characteristics in bottom water reservoirs containing interbeds needs to be strengthened. In this study, water flooding experiments with different placements of the interbeds were conducted using a two-dimensional (2D) vertical model. The results demonstrated that the interbeds make the bottom water flow upward more evenly, resulting in decreased incursion speed, increased displacement area, and better displacement effect. Moreover, compared with the tilted interbed model, the horizontal model has a 6% higher oil recovery rate, exhibiting a better oil displacement effect. The results presented herein will provide important guidance on water control in bottom-aquifer oil reservoirs containing interbeds and will promote unconventional petroleum resources recovery.

Analysis and experimental study on resistance-increasing behavior of composite high efficiency autonomous inflow control device

Bottom water coning is the main reason to reduce the recovery of horizontal bottom water reservoir. By water coning, we mean the oil-water interface changes from a horizontal state to a mound-shaped cone and breaks through to the wellbore. Autonomous inflow control device (AICD) is an important instrument maintain normal production after bottom water coning, however, the resistance increasing ability of the swirl type AICD is insufficient at present, which seriously affects the water control effect. Aiming this problem, this paper designs a multi-stage resistance-increasing and composite type AICD. The separation mechanism of oil-water two phases in this structure, the resistance form of oil-water single phase and the resistance-increasing principle of water phase are analyzed. Establishing the dual-phase multi-stage separation and resistance-increasing model, and verified by measuring the throttling pressure drop and oil-water volume fraction of the AICD, it is found that the composite type AICD has the effect of ICD and AICD at the same time, which can balance the production rate of each well section at the initial stage of production, delay the occurrence of bottom water coning. In the middle and later stages of production, water-blocking can be effectively increased to achieve water control and stable production. After structural sensitivity analysis, the influence law of various structural parameters on the water control performance of composite AICD was obtained. The simulation calculation results show that, compared with the existing swirl type AICD, composite AICD has higher sensitivity to moisture content, the water phase throttling pressure drop is increased by 4.5 times on average. The composite AICD is suitable for the entire stage of horizontal well production.

Mathematical Modeling of Prediction of Horizontal Wells with Gravel Pack Combined with ICD in Bottom-Water Reservoirs

During the development of horizontal wells in bottom-water reservoirs, the strong heterogeneity of reservoir permeability leads to premature bottom-water breakthroughs at locations with high permeability in the horizontal wellbore, and the water content rises rapidly, which seriously affects production. To cope with this problem, a new technology has emerged in recent years that utilizes gravel filling to block the flow in the annulus between the horizontal well and the borehole and utilizes the Inflow Control Device (ICD) completion tool to carry out segmental water control in horizontal wells. Unlike conventional horizontal well ICD completions that use packers for segmentation, gravel packs combined with ICD completions break the original segmentation routine and increase the complexity of the production dynamic simulation. In this paper, the flow in different spatial dimensions, such as reservoirs, gravel-packed layers, ICD completion sections, and horizontal wellbores, is modeled separately. Furthermore, the annular pressures at different locations are used as the solution variable for the coupled solution, which realizes the prediction of oil production, water production, and the water content of gravel packs combined with ICD completion of horizontal wells. The model is used to calculate the effects of different crude oil viscosities, different reservoir permeabilities, different permeabilities of gravel-packed layers, and different development stages on the water control effects of gravel packs combined with ICD completions and conventional ICD completions under field conditions.

Polymer Gel for Water Shutoff in Complex Oil and Gas Reservoirs: Mechanisms, Simulation, and Decision-Making

Summary Gel treatment is often used for water shutoff in high water-cut oil or gas wells. Although the properties and usage methods of gel have been well documented by different investigators, gel treatment performance is not always satisfactory in field application, especially in oil or gas reservoirs with complex conditions, such as strong bottomwater reservoirs, high-permeability-ratio oil reservoirs, and fractured gas reservoirs. In this work, we attempt to improve gel treatment application in complex situations according to the causes of disappointing performance, including unreliable numerical simulation and the misapplication of experiences. We propose a new numerical simulation method of gel treatment mechanisms and verify it by improving the acquiring method of inaccessible pore volume (IAPV), dynamic polymer adsorption (DPA), and the simulation method of disproportionate permeability reduction (DPR). The performance and optimization measures of gel treatment in different types of complex oil and gas reservoirs are discussed extensively. Moreover, the dominant influencing factor of the gel treatment effect is determined by gray relation analysis to provide more direct and effective suggestions for field application. The results suggest that the improved access methods for IAPV and DPA can help to obtain more precise parameters easily to construct a numerical gel model. In addition, the new DPR simulation method, which considers oil or gas blocking, reduces the overestimation of gel DPR ability obtained with the conventional method. The misapplication of gel treatment experience probably causes a disappointing response, for example, gel treatment time had opposite influences on water shutoff in strong bottomwater reservoirs and high-permeability-ratio oil reservoirs, and the experience of reservoir thickness in oil reservoirs was not suitable for gas reservoirs. Furthermore, the major factors of gel treatment are varied in different oil and gas reservoirs, demonstrating that primary evaluation indicators for candidate wells are not permanent.

Fluidic Diode AICD Characteristic Curve Testing and Mathematical Modeling

In order to investigate an efficient water control method suitable for the bottom water occurring during the production process of horizontal wells in bottom water reservoirs, the characteristic curves of a Fluidic Diode AICD (Automatic Inflow Control Device) were tested, and a mathematical modeling method is proposed. First, the working principle of a Fluidic Diode AICD was analyzed; subsequently, a Fluidic Diode AICD test platform was designed and built independently, and pressure test experiments of the Fluidic Diode AICD under different flow conditions were carried out to obtain characteristic curves of the Fluidic Diode AICD. Finally, a mathematical model of the flow–pressure drop characteristic curves of the Fluidic Diode AICD was developed and applied to the simulation of water control production in horizontal wells in bottom water reservoirs. The results of the study showed that the Fluidic Diode AICD produces a more significant pressure drop under high water content conditions, and has a better oil and water stabilization function in production. In this study, the reservoir flow, annulus flow, AICD flow, and horizontal wellbore flow are considered, and an integrated coupling model for horizontal wells in bottom water reservoirs is established. This study provides a basis for using Fluidic Diode AICDs in horizontal wells in bottom water reservoirs.

Water Invasion Prediction Method for Edge–Bottom Water Reservoirs: A Case Study in an Oilfield in Xinjiang, China

Clarifying the water invasion rule of edge and bottom water reservoirs can adjust the reservoir development mode and improve the recovery factor of edge and bottom water reservoirs in a timely manner. Influenced by the size of a reservoir water body, energy intensity and reservoir seepage capacity, the change model of reservoir water influx basically belongs to the exponential growth model of the GM (1,1) model or the self-constraint growth model of the logistic model. The above two models are used to predict and analyze the water inflow of edge and bottom water reservoirs, respectively, and it is found that the change in water inflow of the reservoir with sufficient edge and bottom water energy is more consistent with the prediction results of the GM (1,1) model, but it has a large error compared to the prediction results of the logistic model. The change in water influx in the reservoir with insufficient edge and bottom water energy is consistent with the prediction results of the logistic model and GM (1,1) model. The research shows that the strength of edge and bottom water energy of the reservoir can be determined by analyzing the error of the logistic model in predicting water influx. If we focus on the change in reservoir water influx, the improved GM (1,1) model formed by a Newton parabola interpolation polynomial is used to optimize its background value, which can further improve the prediction accuracy and reduce the prediction error of water inflow of edge and bottom water reservoirs. The method in this paper has certain reference significance for studying the water invasion rule and energy intensity of edge and bottom water reservoirs.

Research on Production Performance Prediction Model of Horizontal Wells Completed with AICDs in Bottom Water Reservoirs

With the advancement of completion technology for horizontal wells in bottom water reservoirs, Autonomous Inflow Control Devices (AICDs), which have achieved good results in recent years, have been widely used in the oil fields of the eastern South China Sea. Although some mathematical methods can be used to predict the production performance of horizontal wells, there is no dynamic prediction method for the production performance of horizontal wells completed with AICDs. In this work, a mathematical model of porous flow in the reservoir, nozzle flow in the AICD, and pipe flow in the horizontal well is established, and then a new model is presented for predicting the dynamic performance of horizontal wells completed with AICDs in bottom water reservoirs. The new coupling model is compared with two horizontal wells completed with AICDs in the bottom water reservoirs of the eastern South China Sea, and the results indicate that the accuracy of the new model is sufficiently high to provide theoretical support for the further prediction of horizontal wells in the eastern South China Sea.

Study on the mechanism of improved oil recovery by nitrogen foam flooding in bottom water reservoirs

There are abundant bottom water reservoirs in China. Unlike conventional oil reservoirs, bottom water reservoirs have various problems, such as early water breakthrough, short water-free oil recovery period, and rapid water cut increase. For example, during water flooding, the injected water easily breaks into the bottom water and does not effectively displace the upper crude oil. The recovery rate is generally low. Based on this phenomenon, an experimental study of nitrogen foam flooding in bottom water reservoirs is conducted in this paper. The seepage characteristics of nitrogen foam in oil and water layers are studied through one-dimensional core tube experiments. Through two-dimensional plate oil displacement experiments, we have revealed the fluid migration and distribution characteristics in the plane and vertical directions during nitrogen foam flooding in bottom water reservoirs; additionally, we have summarized the mechanisms of nitrogen foam in bottom water reservoirs involved in improving oil recovery characteristics. The research results show that the seepage resistance of foam in the water layer is much greater than that in the oil layer, effectively increasing the displacement strength of the oil layer. During the development stage of bottom water flooding in bottom water reservoirs, the water cut increases rapidly, the bottom water coning is obvious, and the residual oil is mainly distributed between the oil wells and the upper part of the oil layer near the wellbore. During nitrogen foam flooding, the foam enters the water layer to form an effective plug so that the subsequent foam is diverted into the oil layer; additionally, the oil is displaced laterally to the production well for production. When the foam enters the oil layer, it defoams and floats to form a secondary gas cap; this effect causes displacement of the residual oil at the top and effectively improves the displacement efficiency by weeping volume of the injected fluid”

Model for Predicting Horizontal Well Transient Productivity in the Bottom-Water Reservoir with Finite Water Bodies

To better understand the horizontal well transient productivity in the bottom-water reservoir with finite water bodies, the horizontal well transient productivity model for the bottom-water reservoir with finite water-body multiple was developed using Green’s function and potential superposition method. Laplace transforms, Fourier transforms, superposition of point source, and Duhamel principle were used to obtain the transient productivity of the horizontal well, and the transient productivity of the horizontal well in real space was obtained by the Stehfest numerical inversion method. The typical pressure response curve and dimensionless productivity curves were plotted. The effects of the water-body multiple, the distance between the horizontal well and oil–water contact, and the skin factor, were analyzed. Six main flowing stages were divided for horizontal wells in the bottom-water reservoir with finite water bodies. When the water body multiples are zero or tend to infinity, the results obtained from the model are consistent with the calculations by the conventional top-bottom closed reservoir model or infinite rigid bottom-water reservoir model, respectively, and the pressure dynamic for the finite water body falls in between both. With the increase in the water body multiples and the decrease in distance between the horizontal well and the oil–water contact, and the horizontal well productivity decreases slowly. With the increase in the skin factor, the initial productivity decreases; moreover, the skin factor has a great influence on the initial productivity of the horizontal well, while the later influence gradually decreases. Accurate horizontal well productivity prediction in the bottom-water reservoir with finite water bodies provides a strong basis for horizontal well deployment, design optimization, and formulation of development policy.

Study on Remaining Oil at High Water Cut Stage of the Offshore Strong Bottom Water Reservoir

Study on Remaining Oil at High Water Cut Stage of the Offshore Strong Bottom Water Reservoir

Macro- and Microanalysis on Noncondensable Gas Antiwater Invasion in a Bottom Water Reservoir with a Rupturable Interlayer.

Developing a bottom-water reservoir with rupturable interlayers is a significant challenge. This paper used a 2D visualization model to study the seepage characteristics of gas–water in two phases during noncondensable gas antiwater invasion. On this basis, the mechanisms of antiwater invasion and enhanced oil recovery (EOR) were summarized. The results show that bottom water advances from the crack of the interlayer to the oil layer, leading to a profile of radial flow. The major swept area occupies the scope near the horizontal well and the oil layer’s middle part. Therefore, a lot of remaining oil distributes beside the crack of the interlayer. Noncondensable gas preferentially flows into the water-swept area due to a lower seepage resistance. Under gravity differentiation, the dispersed gas displaces the invaded bottom water downward, inhibiting water from invading and increasing the oil production rate. These studies provide practical guidance for analyzing bottom-water invading processes and designing suitable measures to develop such reservoirs.

Research and Application of Bottom Water Control and Suppression Technology by CO2 Huff-and-Puff

In order to solve the problems about rapid increasement rate of water cut and large production decline in bottom water heavy oil reservoir due to active bottom water and high crude oil viscosity, the research on CO2 huff-and-puff technology is carried out. The results showed that the mechanism of CO2 huff-and-puff was mainly to reduce the viscosity of heavy crude oil, carbonate reacted with bottom water and formed interlayer to achieve viscosity reduction and precipitation. The comprehensive water cut was decreased by 35%, and the average oil production of a single well was increased by 3∼4 times. Therefore, CO2 huff-and-puff technology was one of technologies about bottom water control and oil production stabilization, and it is of great significance to enhance oil production in heavy oil bottom water reservoirs.

Application of Eurytopic Water Drive Curve to Enhance Liquid in Strong Bottom Water Reservoir: A Case Study of D Oilfield in Bohai Guantao Formation

Application of Eurytopic Water Drive Curve to Enhance Liquid in Strong Bottom Water Reservoir: A Case Study of D Oilfield in Bohai Guantao Formation

Investigation on the water-coning control by CO2 injection in strong bottom water reservoir

The crestal CO2 injection can be used to control the flow of water in a strong bottom water reservoir. Pressure-Volume-Temperature and relative permeability studies were done under formation circumstances (50 MPa, 110 °C) to elucidate the mechanism of water-coning regulation. The findings of the PVT test demonstrated that CO2 might shift the water phase downward, so regulating water-coning and lowering the viscosity of the oil, thereby preventing water break. The results of the relative permeability test indicated that CO2 could reduce the relative permeability of brine, increase the relative flow capacity of crude oil, form a CO2-oil miscible bank concurrently, increase the efficiency of oil displacement by water flooding, and inhibit the formation of water-coning. An appropriate strong bottom-water block was chosen as a trial location for evaluating the water-coning control by CO2 injection. The results suggested that crestal CO2 injection was more successful in reducing water cut than the basic gravity effect. The results also indicated that CO2 injection is a more effective method of controlling water-coning than water plugging.