New Insights into the Low Salinity Water Injection Effect on Oil Recovery from Carbonate Reservoirs (original) (raw)
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International Petroleum Technology Conference, 2014
This paper investigates the combined effect of injecting low salinity water (LSWI) and carbon dioxide (CO 2 ) on oil recovery from carbonate cores. The combined effect of LSWI and CO 2 injection on oil recovery was predicted by performing several synthetic 1D simulations using measured reservoir rock and fluid data. These simulations included the effect of salinity on both miscible and immiscible continuous gas injection (CGI), simultaneous water-alternating-gas (SWAG), constant wateralternating-gas (WAG), and tapered (WAG). For SWAG and constant and tapered WAG, both seawater and its dilutions were simulated, and the CO 2 was injected above the minimum miscibility pressure. Baker's three-phase relative permeability model was modified to account for the effect of salinity on the water/oil relative permeability.
Mechanisms behind low salinity water injection in carbonate reservoirs
2014
History matching of recently published corefloods for low salinity water injection. Investigating the best way of history matching low salinity water injection effect on oil recovery. Highlighting important parameters that should be considered in modeling low salinity water injection effect in carbonates. Wettability alteration is still believed to be the main mechanism underlying the incremental oil recovery by LSWI. Oil endpoint relative permeability is more sensitive to the LSWI effect than is water endpoint relative permeability.
Journal of Geophysics and Engineering
Connate water saturation and its composition, as well as the salinity of injected water, have significant impact on the performance of low salinity water injection (LSWI). Due to the lack of experimental data and difficulties in performing experiments on carbonate rocks, the mechanisms and impact of pertinent parameters involved in the low salinity water flooding in carbonate oil reservoirs is not well understood. In this study, several core flood experiments were conducted on tight carbonate rocks under highly controlled conditions, and using seawater at various dilution ratios as the injected and connate water. The cores were initially established with different connate waters, in terms of saturation and salinity, and the injection scenarios were carried out under secondary and tertiary stages at various salinities. Oil recovery as well as composition and pH of effluent brine were measured to investigate the impact of connate water and salinity on LSWI. The results depicted that oil recovery in the secondary injection stage is maximum for the highest connate water saturation and lowest connate water salinity. Hence, both the salinity of the injected brine and the salinity and saturation of connate brine play a significant role in the performance of LSWI in carbonate rocks. In the tertiary scenario, the highest oil recovery was obtained while both the saturation and salinity of the connate water were minimal. A new mechanism regarding ion exchange and wettability alteration processes was proposed based on ion tracking analysis.
Mechanisms Behind Low Salinity Water Flooding in Carbonate Reservoirs
SPE Western Regional & AAPG Pacific Section Meeting 2013 Joint Technical Conference, 2013
The low salinity water injection method (LoSal) has become one of the important research topics in the oil industry because of its enormous possible advantages. The objective of this paper is to investigate the mechanism behind the LoSal effect on oil recovery through data matching. The UTCHEM simulator was used to match the cycles of the injected seawater and different dilutions of the latter for two recently published coreflooding experiments. The result from the history matching revealed that the wettability alteration mechanism is believed to be the main contributor to LoSal. Based on this finding, an analytical model for oil recovery predictions can be developed.
Journal of Petroleum Science and Engineering, 2020
Low-salinity waterflooding (LSF) is a relatively simple and cheap Enhanced Oil Recovery technique in which the salinity of the injected water is optimized to improve oil recovery over conventional waterflooding. Sulfate-rich as well as diluted brines have shown promising potential to increase oil production in limestone core samples. To quantify the low-salinity effect, spontaneous imbibition and/or waterflooding experiments have been reported. This paper combines spontaneous imbibition, centrifuge and unsteady state (USS) coreflooding experiments to investigate low-salinity effects in carbonate samples. The experimental study used three brine compositions to investigate low-salinity effects. A high-saline Formation-water (salinity of 183.4 g/l), Seawater (43.8 g/l) and 100-times Diluted-seawater (0.4 g/l). Initially, a sequence of spontaneous imbibition experiments was conducted to screen the impact of connate and imbibing water composition on spontaneous oil recovery. After completing the spontaneous imbibition tests, the samples were drained inside a centrifuge to determine the impact of brine composition on residual saturation and capillary pressure. Moreover, three USS corefloodings were conducted to test the different brine compositions in secondary and tertiary injection mode. The spontaneous imbibition, centrifuge method and coreflooding tests showed a consistent trend. Compared to Formation-water and Seawater , Diluted-sea water demonstrated the most promising potential to recover oil efficiently. The numerical part of the study includes the transparent development of a numerical centrifuge and coreflooding model on the top of the open-source simulator DuMu x. The mathematical model formulation demonstrates that a simple numerical approach is sufficient to history match the centrifuge and coreflooding experiments. In line with the experimental data, the numerically derived capillary pressure and relative permeability showed an increasing water-wetting behavior as the salinity of the imbibing/injection water decreased. All implemented numerical models were validated against the commercially established Cydar software.
Wettability Alteration during Low-Salinity Waterflooding in Carbonate Reservoir Cores
All Days, 2014
Production enhancement by low-salinity waterflood in carbonate formations is a subject of intense speculation. Several mechanisms are attributed to enhanced oil recovery by low-salinity waterflooding in carbonate formations. Review of experimental data in the literature indicates that the main mechanism involves interaction of Na+, Cl−, Ca2+, Mg2+, SO42− and crude oil carboxylate ions (R-COO−) with the rock in the electrical double layer (EDL) near the surface of carbonate pores, leading to wettability alteration.In this study, we performed four seawater floods in heterogeneous low-permeability carbonate cores followed by low-salinity floods. The core permeability is between 0.5 to 1.5 md, and porosity in the range of 18 to 25%. Cores were aged for eight weeks at reservoir pressure and temperature. We also conducted pendant drop oil-brine IFT measurement, and captive oil-droplet contact angle at different brine salinity, with and without the presence of surfactant.The carbonate core...
Geochemical modeling of engineered water injection effect on oil recovery from carbonate cores
Journal of Petroleum Science and Engineering, 2018
In the field of enhanced oil recovery, the engineered/low salinity water injection (EWI/LSWI) is one of the promising development in recent years. Several mechanisms describing the EWI/LSWI recovery process have been suggested without a common consensus. Wettability alteration have been considered as the prime reason behind the incremental oil recovery; however, several other possible mechanisms are also suggested. This paper investigates the effect of engineered water injection (EWI) on oil recovery from carbonates cores along with recovery, pH and effluent-ion predictions, which is based on numerical simulations using laboratory coreflood data. An EWI model is proposed based on multi-ion exchange for capturing the incremental oil recovery by EWI in carbonates. The model includes geochemical reactions, homogeneous (aqueous) and heterogeneous (precipitation/dissolution and ionic exchange reactions), as well as the resulting wettability alteration in carbonates. Oil recovery, pressure drop, pH, and effluent-ion were successfully history match and the results showed there is an improvement in oil displacement as EW is injected. Also, the findings of this study were supported by fractional flow analysis. This work provides more insight into the benefits of EWI and hence, supports new field applications.
SPE Improved Oil Recovery Conference, 2016
Several laboratory studies and some field trials have already demonstrated the potential of lowering the injected brine salinity and/or manipulating composition to improve oil recovery in carbonate reservoirs. Laboratory SCAL tests such as coreflooding and imbibition are key steps to screen low salinity waterflood (LSF) for a particular field to (i) ensure that there is LSF response in the studied rock/oil/brine system, (ii) find the optimal brine salinity, (iii) extract relative permeability curves to be used in the reservoir simulation model and quantify the benefit of LSF and (iv) examine the compatibility of injected brine with formation brine and rock to de-risk any potential scaling or formation damage caused by fines mobilization. This paper presents an extensive LSF SCAL study for a carbonate reservoir and the numerical interpretation of the tests. The SCAL experiments were performed at reservoir conditions using reservoir core plugs, dead crude oil and synthetic brines. The rock was characterized using porositypermeability measurement semi-quantitative X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion capillary pressure (MICP) techniques. The characterization work showed that the plugs can be classified into two groups (uni-modal and bi-modal) based on pore throat size distribution which correlated with porosity-permeability cross-plots. The SCAL experiments were divided in two categories. Firstly, spontaneous imbibition and qualitative unsteady-state (USS) experiments were performed to demonstrate the effect of low salinity brines. In addition, these experiments helped to screen different brines (seawater and different dilutions of seawater) in order to choose the one that showed the most promising effect. Secondly, quantitative unsteady-state (USS) experiments were conducted and interpreted using numerical simulation to extract relative permeability curves for high salinity and low salinity brines by history-matching production and pressure data. The main conclusions of the study are: 1-The spontaneous imbibition and qualitative USS experiments showed extra oil production when switching from formation brine to seawater or diluted seawater subsequently, 2-Oil recovery by LSF can be maximized by injection of brine at a certain salinity threshold, at which lowering the brines salinity further did not lead to additional recovery improvement,
Modeling Earth Systems and Environment, 2020
Waterflooding operation is one of the conventional and well-tested methods to improve oil recovery. However, in an oilwet reservoir system, high water mobility is a primary concern resulting in lower oil production. This study, hence, aims to investigate the impact of injection water salinity changes on oil production and water mobility. With this, the variation of wettability and production of salt due to changing injection water salinity is also a part of this study. This study initiates with generating a three-dimensional, two-phase oil and water model. The reservoir is initially in the oil-wet stage. During the simulation, the relative permeability curves are adjusted to mimic the wettability alteration from oil-wet to water-wet. Initially, the impact of salinity on the oil recovery, water mobility, and salt production is studied through the sensitivity analysis between the low-saline and high-saline water injection. Later, a comparison of two injection strategies, including direct line and five-spot, is conducted to determine an effective injection technique for the comprehensive analysis of salinity changes on a waterflooding project. At last, the sensitivity analysis of different water salinity ranges of 0-35,000 ppm has been performed to compare the water salinity effects on water mobility, oil production, and salt production. It has been found through simulation that the oil recovery is improved significantly as the salinity of injected brine decreases below 5000 ppm. The oil recovery factor obtained while decreasing the salinity is as high as 72%. Moreover, the water cut is highly delayed as the salinity of water decreases. Furthermore, salt production is significantly lowered at the production well. Hence, reducing the salinity of injection water proved to be an effective strategy to recover more oil from an oil-wet reservoir.