A Novel Trilinear Flow Model for Capturing Dynamic Behavior of Water Flooding in Core Plug with Different Fracture Inclinations in Carbonate Reservoirs

The purpose of this study is to introduce a new three-linear flow model for capturing the dynamic behavior of water flooding with different fracture occurrences in carbonate reservoirs. Low-angle and high-angle fractures with different occurrences are usually developed in carbonate reservoirs. It is difficult to simulate the water injection development process and the law of water flooding is unclear, due to the large variation of the fracture dip. Based on the characteristics of water flooding displacement streamlines in fractured cores with different occurrences, the matrix is discretized into a number of one-dimensional linear subregions, and the channeling effect between each subregion is considered in this paper. The fractures are divided into the same number of fracture cells along with the matrix subregion, and the conduction effect between the fracture cells is considered. The fractured core injection-production system is divided into three areas of linear flow: The injected fluid flows horizontally and linearly from the matrix area at the inlet end of the core to the fracture and then linearly diverts from the fracture area. Finally, the matrix area at the outlet end of the core also presents a horizontal linear flow pattern. Thus, a trilinear flow model for water flooding oil in fractured cores with different occurrences is established. The modified BL equation is used to construct the matrix water-flooding analytical solution, and the fracture system establishes a finite-volume numerical solution, forming a high-efficiency semianalytical solution method for water-flooding BL-CVF. Compared with traditional numerical simulation methods, the accuracy is over 86%, the model is easy to construct, and the calculation efficiency is high. In addition, it can flexibly portray cracks at any dip angle, calculate various indicators of water flooding, and simulate the pressure field and saturation field, with great application effect. The research results show that the greater the fracture dip angle, the higher the oil displacement efficiency. When the fracture dip angle is above 45°, the fracture occurrence has almost no effect on the oil displacement efficiency. The water breakthrough time of through fractures is earlier than that of nonthrough fractures, and the oil displacement efficiency and injection pressure are more significantly affected by the fracture permeability. With the increase of fracture permeability, the oil displacement efficiency and the injection pressure of perforated fractured cores dropped drastically. The findings of this study can help for better understanding of the water drive law and optimizing its parameters in cores with different fracture occurrences. The three-linear flow model has strong adaptability and can accurately solve low-permeability reservoirs and high-angle fractures, but there are some errors for high-permeability reservoirs with long fractures.

Displacement of oil by SiO2-nanofluid from a microporous medium: microfluidic experiments

In this work, the process of displacing oil from a microfluidic chip that simulates a porous medium is studied. Experimental photographs of the process of oil displacement by water and SiO2-nanofluid are presented. It is shown that the use of nanofluid increases the oil displacement efficiency by 16%.

Research of Phase Behavior in Natural Gas Drive Process and Its Application in T_D Reservoir with HTHP

Different from other gas drive processes, phase behavior performs more significant roles in natural gas drive process. The main reason is that more severe mass transfer effect and similar phase solubility effect have been caused by multicomponent interaction. This paper provides a series of methods to study the phase behavior in natural gas drive process, aiming to reveal further mechanism and give technical supports to the on-site practice in T_D Reservoir with HTHP. Four key parameters of natural gas drive have been determined. Firstly, laboratory compounding method has been improved to obtain real components of formation fluids and actual injected gas at formation condition (140°C, 45MPa). Secondly, 19 sets of slim tube test has been carried to determine MMP (minimum miscible pressure) and the injected gas components ensuring miscibility. Thirdly, swelling test and laser method have been used to separately obtain the viscosity reduction degree and solid deposition effects. Finally, multiple contact test has been carried to describe the miscibility behavior. All the above have been applied in T_D Reservoir. Conclusions could be drawn from the results obtained by the methods above. Firstly, swelling capacity of crude oil could be enhanced by natural gas for the formation volume factor of crude oil in T_D Reservoir increased by 57% and the viscosity decreased by 83% after natural gas injection. Secondly, MMP of dry gas and crude oil in T_D Reservoir is 43.5MPa with a miscible displacement efficiency above 90% (>30% compared with immiscible displacement efficiency), and the content of N2+C1 should be controlled over 88%. Thirdly, results of 5 levels contact experiments shows that miscibility behavior of natural gas and oil from T_D Reservoir performs an evaporative-condensate composite miscible process in which the condensate miscible process takes the lead. Finally, obvious solid point has not been observed in natural gas drive process of crude oil from T_D Reservoir at the formation temperature, and the effect of solid deposition on the fluid flow in formation could be ignored because of trace amount of solid solution (<1mg/ml) and minute formation permeability damage (<8%). The achievements above have been applied in T_D Reservoir as one of the important technical means supporting over 350,000 tons increased production by natural gas drive. A systematic methods have been reorganized to research the phase behavior in natural gas drive process and half of these methods mentioned above get partially improvement. These physical simulation experiments have covered most mainly processes and the key parameters in reservoirs with HTHP and natural gas drive, including mass transfer, viscosity, expansion, volume coefficient, MMP, miscibility behavior and solid deposition. Every experiment gives a quantitative analysis which possesses satisfied practicability in field application.

Litho-Based Pore Scale Waterflooding in Carbonate Reservoirs: A Holistic Approach to Predict Displacement Efficiency

Grainstones deposited on carbonate ramps are excellent petroleum reservoir formations and are important for energy needs. Waterflooding is routinely used to augment oil recovery and many carbonate fields have long production histories. Future management of these "mature" assets requires knowledge of how oil production can be sustained and enhanced but requires understanding the pore-scale displacement processes. Despite decades of waterflooding in carbonate oilfields a plausible displacement efficiency prediction is not yet trivial. To evaluate waterflooding economics, it is crucial to know the residual oil saturation (Sor) and where oil is entrapped by capillarity in the reservoir. Microfluidic waterflooding experiments provide a means to visualize pore-scale phenomena within different carbonate minerals (calcite, dolomite, and gypsum) and petrographic textures, to estimate microscopic displacement efficiency. By using analogues of carbonate ramp reservoir-lithologies (in terms of texture, unstructured-irregular pore networks and varied mineralogical compositions) realistic evaluations of displacement efficiency were determined for different mineralogical compositions. The quantitative test results matched closely Arab formation SCAL published data. It was determined that multi-mineralic grainstones undergoing waterflood likely experience contemporaneous imbibition and drainage, giving rise to complex multiphase flow due to the existence of different states of wettability. This wettability contrast induces "capillary jumps" across wettability-boundaries at the interface between different lamina or textures. These "capillary leaps" account for increase in oil recovery as they occur but leave behind bypassed oil. Consequently poly-mineralic arrangements have a lower oil recovery compared to mono-mineralic cases. It was observed that distinct Sor are achieved at different injected pore volumes, despite sharing similar porosity & permeability, thus the relationship between Sor and porosity/permeability is weak. Thus, predicting waterflooding efficiency requires the different carbonate minerals Sor to be incorporated in dynamic simulation.

Molecular Simulation of Methane Sorption onto Kerogen Surface of Shale in Presence of Surfactant

Shale reservoirs, despite having abundance in hydrocarbon storage, offer significant challenges in terms of understanding the pore-scale and reservoir-scale phenomenon. Typically, hydraulic fracturing treatment is implemented to improve hydrocarbon productivity through the injection of fracturing fluid to induce the breakdown of the formation to create fractures, hence allowing a flow conduit for hydrocarbon to be produced at a higher flow rate of oil and/or gas. In this work, molecular dynamics (MD) simulation using GROMACS were utilized to create a 3D model comprised of methane (CH4), surfactant and graphite. Surfactant, as represented by the cationic cetyl trimethyl ammonium bromide (CTAB) was added along with water to represent water-based visco-elastic surfactant (VES) as an additive to reduce the surface tension of hydrocarbon to shale (represented by graphene). A realistic molecular model was created to examine the interaction of CTAB towards the adsorption pattern of methane onto graphene, in order to reveal the displacement efficiency of methane after wettability modification due to the effect of surfactant on the graphene on a nanoscale. The findings suggest that addition of CTAB as surfactant may enhance the production of methane though the reduction of IFT and adsorption capability of methane to the wall of shale. The result yielded consistent trends, where methane's tendency to stick to the adsorption site (at approximately 1.5 nm from the center of the system) was reduced and more methane molecules were accumulated at the center of the pore space. This study has uncovered the adsorption process and the effect of CTAB in altering the sorption behavior of methane towards shale. This would contribute to the enhancement of long-term shale gas production by providing more information on salinity and pressure sensitivity, enabling extraction to be done at a lower cost.

Core-to-Field-Scale Simulations of Polymer Viscoelastic Effect on Oil Recovery Using the Extended Viscoelastic Model

Being one of the most commonly used chemical EOR methods, polymer flooding can substantially improve both macroscopic and microscopic recovery efficiencies by sweeping bypassed oil and mobilizing residual oil, respectively. However, a proper estimation of incremental oil to polymer flooding requires an accurate prediction of the complex rheological response of polymers. In this paper, a novel viscoelastic model that comprehensively analyzes the polymer rheology in porous media is used in a reservoir simulator to predict the recovery efficiency to polymer flooding at both core- and field-scales. The extended viscoelastic model can capture polymer Newtonian and non-Newtonian behavior, as well as mechanical degradation that may take place at ultimate shear rates. The rheological model was implemented in an open- source reservoir simulator. In addition, the effect of polymer viscoelasticity on displacement efficiency was also captured through trapping number. The calculation of trapping number and corresponding residual-phase saturation was verified against a commercial simulator. Core-scale tertiary polymer flooding predictions revealed the positive effect of injection rate and polymer concentration on oil displacement efficiency. It was found that high polymer concentration (>2000 ppm) is needed to displace residual oil at reservoir rate as opposed to near injector well rate. On the other hand, field-scale predictions of polymer flooding were performed in a quarter 5-spot well pattern, using rock and fluid properties representing the Middle East carbonate reservoirs. The field-simulation studies showed that tertiary polymer flooding might improve both volumetric sweep efficiency and displacement efficiency. For this case study, incremental oil recovery by polymer flooding is estimated at around 11 %OOIP, which includes about 4 %OOIP residual oil mobilized by viscoelastic polymers. Furthermore, the effect of different parameters on the polymer flooding efficiency was investigated through sensitivity analysis. This study provides more insight into the robustness of the extended viscoelastic model as well as its effect on polymer injectivity and related oil recovery at both core- and field-scales. The proposed polymer viscoelastic model can be easily implemented into any commercial reservoir simulator for representative field-scale predictions of polymer flooding.

Novel Automated Light Foam Cementing Set-Up Brings Operational Efficiency to Major Operator in Norwegian North Sea Sector

As oil and gas operators are constantly looking for ways to increase efficiency in their operations, one area of well construction that is becoming increasingly popular is in the field of foam cementing. Foamed cement slurries are designed to have low density with relatively high compressive strength to enable operators accomplish their zonal isolation requirements. In addition, the enhanced slurry mobility of these energized fluids leads to a high displacement efficiency to ensure uniform cement coverage in the annulus. The use of foamed cement slurries particularly for top-hole sections in deep-water environments has increased over the past decade. For large volume jobs such as these, operators utilize the standard Automated Foam Cement System (AFCS) which comprises of high-pressure nitrogen pumps /converter and portable liquid nitrogen tanks. The AFCS automatically controls nitrogen and cement slurry based on the downhole rate and precisely maintains a desired foam cement density. For smaller volume jobs, the main constraint to deploying the standard AFCS is mainly rig deck space limitations, thus a "light foam package" was developed. The light package, fully developed in Norway, maintains the already well-established characteristics of automation from the standard AFCS; with the added benefit of minimizing footprint on board the rig with equipment which includes foam manifold, gas bottle rack and nitrogen control flow valve vs. the conventional liquid nitrogen tanks, pumps, and back up equipment. Other advantages of this set up include much faster rig up time due to smaller and lighter liftsimproved HSE benefits of eliminating liquid nitrogen handling; as well as limiting number of people required offshorefull job accuracy and automatic control with the utilization of mass flowmeters to measure nitrogen and cement rates with precisionrobust system with 100% redundancy of critical components This publication highlights the job details from a light foam job performed on a 30in conductor in a well on the Norwegian Continental Shelf, with the objective to cement the entire conductor length to seabed. This job was conducted in a field where numerous past cement jobs had failed to bring cement up to seabed and top up jobs with grout were the norm to achieve top of cement. With this simplified foam cementing process, the vision is that this kind of system set-up can make foam cementing a reality even in the most remote of locations and/or locations with small deck space, with reduced start-up costs.

The Combined Flooding of Dispersed Particle Gel and Surfactant for Conformance Control and EOR: From Experiment to Pilot Test

The water channeling and excess water production led to the decreasing formation energy in the oilfield. Therefore, the combined flooding with dispersed particle gel (DPG) and surfactant was conducted for conformance control and enhanced oil recovery in a high temperature (100-110°C) high salinity (>2.1×105mg/L) channel reservoir of block X in Tahe oilfield. This paper reports the experimental results and pilot test for the combined flooding in a well group of Block X. In the experiment part, the interfacial tension, emulsifying capacity of the surfactant and the particle size during aging of DPG were measured, then, the conformance control and enhanced oil recovery performance of the combined flooding was evaluated by core flooding experiment. In the pilot test, the geological backgrounds and developing history of the block was introduced. Then, an integrated study of EOR and conformance control performance in the block X are analyzed by real-time monitoring and performance after treatment. In addition, the well selection criteria and flooding optimization were clarified. In this combined flooding, DPG is applied as in-depth conformance control agent to increase the sweep efficiency, and surfactant solution slug following is used for improve the displacement efficiency. The long term stability of DPG for 15 days ensures the efficiency of in-depth conformance control and its size can increase from its original 0.543μm to 35.5μm after aging for 7 days in the 2.17×105mg/L reservoir water and at 110°C. In the optimization, it is found that 0.35% NAC-1+ 0.25% NAC-2 surfactant solution with interfacial tension 3.2×10-2mN/m can form a relatively stable emulsion easily with the dehydrated crude oil. In the double core flooding, the conformance control performance is confirmed by the diversion of fluid after combined flooding and EOR increases by 21.3%. After exploitation of Block X for 14 years, the fast decreasing formation energy due to lack of large bottom water and water fingering resulted in a decreasing production rate and increasing watercut. After combined flooding in Y well group with 1 injector and 3 producers, the average dynamic liquid level, daily production, and tracing agent breakthrough time increased, while the watercut and infectivity index decreased. The distribution rate of injected fluid and real-time monitoring also assured the conformance control performance. The oil production of this well group was increased by over 3000 tons. Upon this throughout study of combined flooding from experiment to case study, adjusting the heterogeneity by DPG combined with increasing displacement efficiency of surfactant enhanced the oil recovery synergistically in this high salinity high temperature reservoir. The criteria for the selection and performance of combined flooding also provides practical experiences and principles for combined flooding.

Effects of Clay Minerals and External Pressures on Imbibition in Shales

Imbibition is an important mechanism of recovery during waterflooding and low flow-back during fracking in shale reservoirs. Experiments were carried out to study the development of imbibition in shale samples. The effects of clay minerals, especially the illite and IS, were mainly investigated and discussed. The imbibition under different pressures was conducted and compared. The influence of clay minerals on imbibition in shale is significant and complex. It is shown that the low content of illite and IS and small capillary force lead to small imbibition mass and speed. Formation of new micro fractures due to the swelling of clay minerals can cause the permeability to increase and the imbibition to be speeded up. The pore structure, the content of IS, and the capillary force affect the imbibition process significantly. The external pressure obviously affects the imbibition speed and the final imbibition mass. The content of clay minerals is more important to the formation of new micro fractures than the external pressure. There is a peak in the curve of displacement efficiency versus the content of either clay minerals or illite and IS. The effect of illite and IS more remarkable.