Modeling of Permeability Reducing Vertical Conformance Treatments

Chemical treatments (usually polymer gels) are commonly used to improve the vertical conformance of oil reservoirs by selectively reducing the permeability in some zones near the well. The resuIts of such treatments have been sporadic and unpredictable. The objective of this study is to define those reservoir characteristics which lead to successful treatments and to provide guidelines for the application of conformance treatments by modeling them with a reservoir simulator-. The computer simulator is the BOAST model, a multiphase, three-. dimensional finite difference model written by Fanchi J. R. et al. and released by the Department of Energy. It was modified in areas such as the restart procedure , the rate allocation scheme, condition of well constraint, interpretation of relative permeability and implicit rate calculation to meet the objectives of this study. Several cases have been run to identify the reservoir properties that strongly influence the outcome of a conformance treatment. These are the vertical permeability, the permeability thickness product contrast between layers, the permeability contrast, and the level of permeability reduction near the injection well. The results presented interpret the test cases and provide a basis for possible implementation of a successful conformance treatment. Finality, a field case is presented in which actual reservoir properties were used to study a conformance treatment.Petroleum and Geosystems Engineerin

Impact of Heterogeneity on the Transient Gas Flow Process in Tight Rock

This work is licensed under a Creative Commons Attribution 4.0 International License.There exits a great challenge to evaluate the flow properties of tight porous media even at the core scale. A pulse-decay experiment is routinely used to measure the petrophysical properties of tight cores including permeability and porosity. In this study, 5 sets of pulse-decay experiments are performed on a tight heterogeneous core by flowing nitrogen in the forward and backward directions under different pressures under pore pressures approximately from 100 psi to 300 psi. Permeability values from history matching are from about 300 nD to 600 nD which shows a good linear relationship with the inverse of pore pressure. A preferential flow path is found even when the microcrack is absent. The preferential path causes different porosity values using differential initial upstream and downstream pressure. In addition, the porosity values calculated based on the forward and backward flow directions are also different, and the values are about 1.0% and 2.3%, respectively, which is the primary novelty of this study. The core heterogeneity effect significantly affects the very early stage of pressure responses in both the upstream and downstream but the permeability values are very close in the late-stage experiment. We proposed that that there are two reasons for the preferential flow path: the Joule–Thomson effect for non-ideal gas and the core heterogeneity effect. Based on the finding of this study, we suggest that very early pressure response in a pulse-decay experiment should be closely examined to identify the preferential flow path, and failure to identify the preferential flow path leads to significant porosity and permeability underestimation

Experimental and Mechanistic Study of Stabilized Dry CO2 Foam Using Polyelectrolyte Complex Nanoparticles Compatible with Produced Water To Improve Hydraulic Fracturing Performance

The amount of fresh water used in hydraulic fracturing can be significantly reduced by employing produced water-compatible supercritical CO2 (scCO2) foams. Foams generated using surfactants only have suffered from long-term stability issues resulting in low viscosity and proppant-carrying problems. In this work, foam lamella stabilization with polyelectrolyte complex nanoparticles (PECNPs) and wormlike micelles (WLMs) is investigated. Electrostatic interactions are studied as the defining factors improving the hydraulic fracturing performance using the PECNP system prepared in produced water. Two oppositely charged polyelectrolytes are investigated to generate a more stable lamellae between the aqueous phase and the scCO2 while degrading in the presence of crude oil. The generated dry foam system is used as a hydraulic fracturing fluid in a tight shale formation. The strong compatibility of the synthesized PECNPs with zwitterionic surfactants prepared in highly concentrated brine in the form of wormlike micelles above critical micelle concentration (CMC) helps develop a highly viscous, dry foam capable of using produced water as its external phase. This foam system improves fracture propagation and proppant transport fracture cleanup compared to the base case foam system with no PECNPs. The formation of PEC–surfactant nanoparticles was verified via zeta potential, particle size analysis, and transmission electron microscopy; the underlying mechanism was identified as electrostatic rearrangement of WLMs along the PECNP’s perimeter or formation of electrostatically bonded micelles with the nanoparticle to create a new enhanced nanoparticle. A Raman spectroscopic model was developed to understand the PECNP–surfactant spectra and subsequent spectroscopic and hence structural changes associated with complexation. Enhanced bulk viscosity and improved foam quality as a result of complexation at the interface was identified with rheometry in addition to sand pack experiments with PECNP–surfactant ratios of 1:9 and 4:6 in 33.3 kppm and 66.7 kppm salinity brine systems, respectively. Enhancement in the shear thinning and cleanup efficiency of the fracturing fluid was observed. Formation damage was controlled by the newly introduced mixtures as fluid loss volume decreased across the tight Kentucky sandstone cores by up to 78% and 35% for scCO2 foams made with PECNP–WLMs in 33.3 and 66.7 kppm salinity brine, respectively. The produced water compatibility and reduction of water disposal presented the prospect of environmentally friendly scCO2 foams for hydraulic fracturing of unconventional reservoirs

Improved Efficiency of Miscible C02 Floods and Enhanced Prospects for C02 Flooding Heterogeneous Reservoirs

The PRRC-modified DOE pseudomiscible reservoir simulator MASTER was used to conduct a systematic investigation of CO2 flooding using horizontal wells in conjunction with foam. We evaluated the effects of horizontal well radius, length, and location on oil recovery through our testing. This work is necessary to provide field predictions for the use of foam and/or horizontal wells. A number of coreflood tests were performed to examine the effect of foam on oil recovery in heterogeneous porous media. Two coaxial composite cores were used to simulate layered formation systems. The first, an isolated coaxial composite core, was used to simulate a layered formation system of which the layers were not in communication. The second, in capillary contact, simulated layers in communication. Preliminary results suggest that oil displacement is more efficient when surfactant solution is used with CO2 to form CO2-foam. Results from both systems indicate the potential of using foam for improving oil recovery in heterogeneous porous media. Since injectivity loss is a problem in a number of gas injection projects, a preliminary investigation of injectivity loss in WAG was performed. A number of tests were carried out to investigate injectivity loss, indicating that for a given rock the injectivity loss depends on oil saturation in the core during WAG flooding. Higher loss was found in cores with high in-situ oil saturations. No injectivity loss was observed with the naturally fractured carbonate core

Laboratory Study of the Reformability of Xanthan/Chromium (Ill) Gels Used in Conformance Treatments

One application of xanthan/chromium(III) gels in vertical conformance treatments is to allow the gel to form on the surface, to be degraded by shear during injection through the tubing and perforations, and to reform in the selected high permeability layers to reduce the horizontal permeability contrast between layers. The success of such an application depends on the ability of the gels to reform after having been degraded by high shearing conditions during placement A study of the behavior of the regelation of xanthan gels that have been degraded by shear was carried out in the laboratory. The shearing mechanism was accomplished by various shearing devices in which the shear intensity and shear duration were adjustable. The initial gelation of gels and regelation of degraded gels were identified by continuously monitoring the change of dynamic viscosities using dynamic oscillatory rheological measurements. The reformability of a gel was determined by the ratio of the recovered dynamic viscosity to the dynamic viscosity prior to the shear degradation.The correlation of reformability of a gel and shearing conditions was made based on the regelation results derived from blender shearing and rheometer shearing. The reformability of a weak gel was found to depend on the shear intensity whereas the reformability of a strong gel was independent of the shear intensity. The effect of shear duration was found insignificant to the reform abilities of both types of gels. Consideration of gel holding time in field application shows that a prolonged gel holding time can lead to the loss of reformability for a strong gel but not for a weak gel.Petroleum and Geosystems Engineerin

Improved efficiency Of miscible CO[sub]2 floods and enhanced prospects for CO[sub]2 flooding heterogenous reservoirs: Quarterly technical progress report, January 1, 1997-March 31, 1997

Task 1: The technical paper, `Assessment of Foam Properties and Effectiveness in Mobility Reduction for C0{sub 2} Foam Floods,` was prepared and presented at the 1997 SPE International Symposium on Oilfield Chemistry. The paper covers five surfactants tested earlier for their foam properties. Work is progressing on evaluating surfactants and their foam properties under high pressure conditions by using a foam durability apparatus. Two surfactants, Witcolate 1259 and Witcolate 1276, were tested in this quarter and the new data were added into our existing database for correlation between foam properties in the bulk phase and in porous media. The new data support the earlier conclusion that foam stability and interfacial tension correlate with selective mobility reduction. Task 2: The changing permeability of the core during a series of foam tests is a significant factor in determining foam coreflood test parameters. A series of tests often requires hundreds of pore volumes of fluids to pass through the core. During this quarter, a new core was developed that should eliminate this problem and provide a constant base line. We ran a series of tests, which showed that this core has a constant permeability, as anticipated. We continued to examine procedures for history-matching production data from C0{sub 2}-foam oil production. The model mechanisms seen are very sensitive to the reservoir description. We have been examining different methods to develop a reservoir description. Task 3: The technical paper, `A Simple and Accurate Method for Determining Low IFT from Pendant Drop Measurements`, was prepared for and presented at the 1997 SPE International Symposium on Oilfield Chemistry. The paper described a new method for IFT determination developed on the basis of a force balance on the lower half of the pendant drop. The method developed is especially accurate for low-IFT systems where wettability effects often render classical LaPlace methods inaccurate. The investigation of C0{sub 2} gravity drainage in fractured reservoirs continues. We have an ongoing experiment using whole core and crude oil under reservoir conditions to investigate the effect of water saturation on the efficiency of C0{sub 2} gravity drainage. Before C0{sub 2} injection was initiated, the core was waterflooded to model a secondary waterflood, producing oil in the imbibition mode. After C0{sub 2} injection, oil production was lower while water was being produced concurrently, and then increased after water production ceased. We believe that excessive free water in the core hindered oil recovery during the earlier stage due to competing two-phase relative permeabilities. After 167 days, oil recovery reached 0.24 OOIP in a low-permeability reservoir core

Improved Efficiency of Miscible CO[sub]2 Floods and Enhanced Prospects for CO[sub]2 Flooding Heterogenous Reservoirs: Quarterly Technical Progress Report, January 1, 1997-March 31, 1997

Task 1: The technical paper, `Assessment of Foam Properties and Effectiveness in Mobility Reduction for C0{sub 2} Foam Floods,` was prepared and presented at the 1997 SPE International Symposium on Oilfield Chemistry. The paper covers five surfactants tested earlier for their foam properties. Work is progressing on evaluating surfactants and their foam properties under high pressure conditions by using a foam durability apparatus. Two surfactants, Witcolate 1259 and Witcolate 1276, were tested in this quarter and the new data were added into our existing database for correlation between foam properties in the bulk phase and in porous media. The new data support the earlier conclusion that foam stability and interfacial tension correlate with selective mobility reduction. Task 2: The changing permeability of the core during a series of foam tests is a significant factor in determining foam coreflood test parameters. A series of tests often requires hundreds of pore volumes of fluids to pass through the core. During this quarter, a new core was developed that should eliminate this problem and provide a constant base line. We ran a series of tests, which showed that this core has a constant permeability, as anticipated. We continued to examine procedures for history-matching production data from C0{sub 2}-foam oil production. The model mechanisms seen are very sensitive to the reservoir description. We have been examining different methods to develop a reservoir description. Task 3: The technical paper, `A Simple and Accurate Method for Determining Low IFT from Pendant Drop Measurements`, was prepared for and presented at the 1997 SPE International Symposium on Oilfield Chemistry. The paper described a new method for IFT determination developed on the basis of a force balance on the lower half of the pendant drop. The method developed is especially accurate for low-IFT systems where wettability effects often render classical LaPlace methods inaccurate. The investigation of C0{sub 2} gravity drainage in fractured reservoirs continues. We have an ongoing experiment using whole core and crude oil under reservoir conditions to investigate the effect of water saturation on the efficiency of C0{sub 2} gravity drainage. Before C0{sub 2} injection was initiated, the core was waterflooded to model a secondary waterflood, producing oil in the imbibition mode. After C0{sub 2} injection, oil production was lower while water was being produced concurrently, and then increased after water production ceased. We believe that excessive free water in the core hindered oil recovery during the earlier stage due to competing two-phase relative permeabilities. After 167 days, oil recovery reached 0.24 OOIP in a low-permeability reservoir core

Improved Efficiency of Miscible CO{sub 2} Floods and Enhanced Prospects for CO{sub 2} Flooding Heterogeneous Reservoirs

This work will examine three major areas in which CO{sub 2} flooding can be improved: fluid and matrix interactions, conformance control/sweep efficiency, and reservoir simulation for improved oil recovery. The first full quarter of this project has been completed. We began examining synergistic affects of mixed surfactant versus single surfactant systems to enhance the properties of foams used for improving oil recovery in CO{sub 2} floods. The purpose is to reduce the concentration of surfactants or finding less expensive surfactants. Also, we are examining the effect of oil saturation on the development of foam in CO{sub 2}-surfactant solution systems. CO{sub 2} flooding of low permeability, vugular, and fracture reservoirs are another major thrust of this project. Work conducted this quarter involved simulating gravity stable floods using large core samples; results showed excellent recovery in a low permeability vugular core

Improved efficiency of miscible CO{sub 2} floods and enhanced prospects for CO{sub 2} flooding heterogeneous reservoirs

This project examines three major areas in which CO{sub 2} flooding can be improved: fluid and matrix interactions, conformance control, sweep efficiency, and reservoir simulation for improved oil recovery. This report discusses the activity during the calendar quarter covering October 1, 1999 through December 31, 1999 that covers mostly the second fiscal quarter of the project's third year. Injectivity experiments were performed on two Indian limestone cores. In tests on the first core, a variety of brine, CO{sub 2} WAG, and oil contaminant injection schemes indicated infectivity reduction due to phase conditions and contamination. The results are only quantitative because of plugging and erosion in the core. To date, tests on the second core have investigated the effects of long-term brine stability on the reduction of fluid-rock interaction, in order to quantify fluid effects on infectivity. The authors continue to develop a new approach in reservoir simulation to improve the history matching process on clusters of PCs. The main objective was to improve simulation of complex improved oil recovery methods, such as CO{sub 2}-foam for mobility control and sweep enhancements. Adsorption experiments using circulation and flow-through methods were used to determine the loss of surfactants for economic evaluation. A sacrificial agent, lignosulfonate, was used to reduce the adsorption of the primary foaming agent in both Berea sandstone and Indian limestone. The lignosulfonate has also shown a chromatograph effect, advancing more rapidly through the reservoir, thus initially adsorbing onto the rock before the primary foaming agent arrives. Therefore, considering the simplicity of operation and economics of reducing the cost of expensive surfactant to improve oil recovery, coinjection of lignosulfonate with the primary foaming agent might be a practical approach to consider for field application