Clogging caused by coupled grain migration and compaction effect during groundwater recharge for unconsolidated sandstone reservoir in groundwater-source heat pump

In unconsolidated sandstone reservoirs,presence of numerous movable grains and a complex grain size composition necessitates a clear understanding of the physical clogging process for effective groundwater recharge in groundwater-source heat pump systems.To investigate this,a series of seepage experiments was conducted under in situ stress conditions using unconsolidated sandstone samples with varying grain compositions.The clogging phenomenon arises from the combined effects of grain migration and compaction,wherein the migration of both original and secondary crushed fine-grain particles blocks the seepage channels.Notably,grain composition influences the migration and transport properties of the grains.For samples composed of smaller grains,the apparent permeability demonstrates a transition from stability to decrease.In contrast,samples with larger grains experience a skip at the stability stage and directly enter the decrease stage,with a minor exception of a slight increase observed.Furthermore,a unique failure mode characterized by diameter shrinkage in the upper part of the sample is observed due to the combined effects of grain migration and in situ stress-induced compaction.These testing results contribute to a better understanding of the clogging mechanism caused by the coupled effects of grain migration and compaction during groundwater recharge in unconsolidated sandstone reservoirs used in groundwater-source heat pump systems.

Quantitative description of characteristics of high-capacity channels in unconsolidated sandstone reservoirs using in situ production data

Quantitative description of the high-capacity channels in unconsolidated sandstone reservoirs, into which water was injected to improve oil recovery, is a hot topic in the field of reservoir development. This paper presents a novel approach to describing quantitatively the characteristics of connected macropores in unconsolidated sandstone reservoirs using in situ production data. Based on physical simulation for formation mechanisms of high capacity channels and interwell tracer test data, a mathematical model was established to describe high-capacity channels by grey correlation theory, flow mechanism of fluid in porous media and reservoir engineering, and a program was developed to describe quantitatively the channel characteristics. The predicted results were consistent with field monitoring data （80%）, so this model could be economically and effectively used to identify high-capacity channels.

Productivity Testing Design Method of Multi-Factor Control for Unconsolidated Sandstone Gas Reservoir

Reservoir safety, testing-string safety, and flow control are key factors that should be considered in deep-water unconsolidated sandstone gas well testing work system. Combined with the feature of testing reservoir, pipe string type and sea area, the required minimum testing flow rate during cleaning up process, as well as minimum test flow rate without hydrate generation, pipe string erosion critical production, the maximum testing flow rate without destroying sand formation and the minimum output of meeting the demand of development was analyzed;based on the above critical test flow rates, testing working system is designed. Field application showed that the designed work system effectively provided good guidance for field test operations;no sand production or hydrate generation happened during the test process;the test parameter evaluated the reservoir accurately;the safe and efficient test operation was achieved.

Advancing sandstone reservoir compressibility prediction:A correlation-driven methodology

This study presents a correlation-based approach for predicting the compressibility of sandstone reservoir rocks.The study proposes a matrix of new empirical equations that significantly improve the precision of measuring the pore volume compressibility,with the most optimal fit of results based on a cubic polynomial model.The accuracy of the calculations was validated through comparison with actual data using root mean square method,and the suggested correlations significantly enhance the precise prediction of rock compressibility in sandstone reservoirs.In this study,the source of data collection is consolidated and unconsolidated sandstone from East Asia offshore oilfields.Accordingly,variations in compressibility with net overburden pressure over the course of the field's lifespan have been examined.The results demonstrate the application of regression analysis in establishing a network of linkages between independent and dependent variables.The proposed correlations for consolidated and unconsolidated sandstones offer a remarkable improvement in the accurate calculation of rock compressibility compared to traditional laboratory procedures,with an average error of 2.5%compared to 5-10%for laboratory measurements.The approach of this study offers a cost-effective and time-efficient alternative to remarkedly enhance the overall performance of sandstone reservoirs in the oil and gas industry.

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage(SAGD)process.A mathematical approach was proposed in this research that fully couples the hydraulic,mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks.The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water.It was found that the predicted bottom hole pressures(BHPs)match closely with the field observed data.An elliptical dilation zone developed around the dual wells with relatively high pore pressure,porosity,permeability and temperature,implying good interwell hydraulic communication between both wells.The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells,though to a lesser extent.In summary,the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

A new method to optimize the fracture geometry of a frac-packed well in unconsolidated sandstone heavy oil reservoirs

The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil.Owing to weakly consolidated formation,sand production is an important problem encountered during oil production in heavy oil reservoirs,for which frac-pack technique is one of the most common treatments.Hence,how to obtain the optimal fracture geometry is the key to increasing well production and preventing sand.Due to the faultiness that current optimization of the fracture geometry only depends on well productivity,fracture-flow fraction was used to describe the contribution of the fracture collecting and conducting fluids from the reservoir.The higher the fracture-flow fraction,the more likely bilinear flow pattern occurs,thus leading to smaller flow resistance and better results in oil productivity and sand prevention.A reservoir numerical simulation model was established to simulate the long-term production dynamic of a fractured well in rectangular drainage areas.In order to reach the aim of increasing productivity meanwhile preventing sand,a new method based on Unified Fracture Design was developed to optimize the fracture geometry.For a specific reservoir and a certain amount of proppant injected to the target layer,there exits an optimal dimensionless fracture conductivity which corresponds to the maximum fracture-flow fraction,accordingly we can get the optimal fracture geometry.The formulas of the optimal fracture geometry were presented on square drainage area conditions,which are very convenient to apply.Equivalent Proppant Number was used to eliminate the impact of aspect ratios of rectangular drainage area,then,the same method to optimize the fracture geometry as mentioned for square drainage areas could be adopted too.

Fluid flow with compaction and sand production in unconsolidated sandstone reservoir

The fluid flow of unconsolidated sandstone reservoir can be affected by compaction and sand production which will damage the reservoir and affect oil well productivity.This study aims to measure how the two factors affect the fluid flow.Firstly,single-phase displacement test was applied to investigate how the permeability changed with compaction.Then two-phase displacement test assessed the influence of compaction on oil production.Finally,the characteristics of fluid flow with compaction and sand production were studied under different water content.The results demonstrate that the reduction of permeability with compaction is irreversible,which will result in lower productivity.In contrast,sand production can increase the permeability at mid and high water content,which slows down the decline of oil production.Generally,the oil well productivity is reduced because of compaction even with sand production,especially when the formation pressure drop varies from 2MPa to 4MPa.Consequently,advance water injection is necessary to keep the formation pressure and oil production during oilfield development of unconsolidated sandstone reservoir.Simultaneously,the study can provide theoretical basis and references for the similar reservoirs.