Experimental Investigation of the Impact of Crude Oil and Rock on Improved Recovery by Low Salinity Water Injection

This study aims to compare the roles of rock and crude oil in improving recovery by low salinity water injection (LSWI) and, particularly, to explore the significance of micro-dispersion formation in LSWI performance. Core samples and crude oil were taken from two carbonate reservoirs (A and B) in Abu Dhabi. The oil samples were selected such that one of them would form micro-dispersion when in contact with low salinity brine while the other would not. A series of coreflood experiments was performed in secondary and tertiary modes under reservoir conditions. First, a core sample from reservoir A was initialized and aged with crude oil from reservoir A and a core sample from reservoir B was initialized and aged with crude oil from reservoir B. The cores were then swapped, and the performance of low salinity injection was tested using rock from reservoir A and crude from reservoir B, and vice versa. For the first set of experiments, we found that the crude oil sample capable of forming micro-dispersion (we call this oil "positive", from reservoir A) resulted in extra oil recovery in both secondary and tertiary LSWI modes, compared to high salinity flooding. Moreover, in the secondary LSWI mode we observed significant acceleration of oil production, with higher ultimate oil recovery (12.5%) compared to tertiary mode (6.5%). To ensure repeatability, the tertiary experiment was repeated, and the results were reproduced. The core flood test performed using "negative" crude oil that did not form micro-dispersion (from reservoir B) showed no improvement in oil recovery compared to high salinity waterflooding. In the "cross-over" experiments (when cores were swapped), the positive crude oil showed a similar improvement in oil recovery and the negative crude oil showed no improvement in oil recovery even though each of them was used with a core sample from the other reservoir. These results suggest that it is the properties of crude oil rather than the rock that play the greater role in oil recovery. These results suggest that the ability of crude oil to form micro-dispersion when contacted with low salinity water is an important factor in determining whether low salinity injection will lead to extra oil recovery during both secondary and tertiary LSWI. The pH and ionic composition of the core effluent were measured for all experiments and were unaffected by the combination of core and oil used in each experiment. This work provides new experimental evidence regarding real reservoir rock and oil under reservoir conditions. The novel crossover approach in which crude oil from one reservoir was tested in another reservoir rock was helpful for understanding the relative roles of crude oil and rock in the low salinity water mechanism. Our approach suggests a simple, rapid and low-cost methodology for screening target reservoirs for LSWI.

Optimum Salt Concentration Design of Low Salinity Water Injection in Tangai Structure at Sukananti Field

Enhanced Oil Recovery (EOR) come up with promising result to endure mature fields production performance and has been proven worldwide in many various methods. Recently, Low Salinity Water Injection evolves as a simply operation and relatively low cost EOR method with wide of research and implementation seem to be proved effective in the past decades. Some laboratory tests have indicated that injecting low salinity water can improve conventional waterflood performance by 5 – 20%. Hence, it introduces a promising idea that Low Salinity Water Injection should be implemented to mature fields in Indonesia for EOR activity. This paper will focus on determining the optimum salt concentration of injection water for low salinity water injection. Low salinity water injection in this study will be acted as a secondary recovery method. The production performance as a result of low salinity water injection was acquired by numerical simulation using tNavigatorTM Simulator. This simulation will be conducted in Tangai Structure at Sukananti Field, South Sumatera Basin, Indonesia with Talang Akar Formation reservoir target. The simulation is conduct with the constraint injection rate of 1,340 BWIPD. The low salinity water is designed by dilution of salt concentration from formation water with 18,000 ppm of concentration. In this case, the sensitivity of low salinity water, mainly amount of salt concentration design, will be conducted in the simulation consisting of using formation water as scenario’s base case and various low salinity water designs which will be limited until 10x of dilution (1,800 ppm). The result of this study concluded that Low Salinity Water Injection achieved more oil recovery than conventional waterflood did. This incremental is caused by wettability alteration due to of salt concentration changes which attract the clay minerals in reservoir through many complex mechanisms. The simulation result shows that injection water with 10x dilution (1,800 ppm) is chosen as an optimum salt concentration design, which gives the best result with gains additional oil recovery and recovery factor about of 118,8 MSTB and 4,9% respectively from a scenario by injecting formation water (18,000 ppm).

http://archives.datapages.com/data/ipa_pdf/2021/IPA21-BC-205.html

Handil Field is a giant mature oil and gas field situated in Mahakam Delta, East Kalimantan Indonesia. Peripheral Low Salinity Water injection was performed since 1978 with extraordinary results. This paper describes the success story of this secondary recovery by low salinity water injection application in the peripheral of Handil field main zone, which successfully increased the oil recovery and brought down the remaining oil saturation beyond the theoretical value of residual oil saturation. Water producer wells were drilled to produce low salinity water from shallow reservoirs 400 - 1000 m depth then it was injected to main zone reservoirs where the main accumulation of oil is situated. This low salinity water reacted positively with the rock properties and in-situ fluids which is described as wettability alteration in the reservoir. It is related to initial reservoir condition, connate water saturation, rock physics and connate water salinity. This peripheral scheme then observed having the sweeping effect on top of pressure maintenance due to long period of injection. The field production performance was indicating the important reduction of residual oil saturation in some reservoirs with continuous low salinity water injection. From static Oil in Place calculation, some reservoirs have high current oil recovery up to 80%. This was proved by in situ residual oil saturation measurement which was performed in 2007 and 2011. It was indicating the low residual saturation as low as 8% - 15%. This excellent result was embraced by a progressive development plan, where water flooding with pattern and chemical injection will be performed later on. The continuation of this peripheral injection is in an on-going development with patterns injection which is called water flooding development. An important oil recovery can be achieved with a simple scheme of low salinity injection, performed in a close network injection, where the water treatment is simple yet significant oil gain was recovered. This innovation technique brings more revenue with less investment compared to chemical EOR injection.