Improving Wateflood Recovery: LoSal™ EOR Field Evaluation

Abstract

This paper reviews the effect of brine composition on LoSalTM EOR waterflood recovery. An improved understanding of the LoSalTM mechanism is presented. Corefloods and single-well tracer tests were performed to evaluate the mechanism and quantify recovery benefits. It was determined that recovery is a function of water chemistry and formation mineralogy. Project economics are significantly enhanced by injecting a slug of low salinity water versus continuous injection. It was determined that a 40% slug by pore volume is fully effective. The work presented in this paper was done to quantify tertiary LoSalTM EOR benefits at the Endicott field located on the North Slope of Alaska. An interwell test is currently underway to unambiguously measure LoSalTM EOR response at field scale. Background The effect of brine composition on waterflooding was first documented by Jadhunandan in 19901 and by Jadhunandan and Morrow in 19912. The first published single well chemical tracer test (SWCTT) results were presented by Webb et al in 20043, and by McGuire et al in 20054. In the past few years numerous core measurements and field tests have been performed at the Endicott Field (Figure 1). A better understanding of the LoSalTM mechanism and encouraging results from field tests at Endicott are evidence that LoSalTM is an emerging EOR technology Endicott was brought on line in 1987. It is a mature offshore oil field located on the North Slope of Alaska. Endicott has been produced with crestal gas re-injection and peripheral water injection. Approximately 10 percent of the produced gas has been used for fuel. Produced reservoir water has been re-injected. Voidage replacement has been accomplished with sea water injection. The salinity and hardness of the reservoir water and the sea water are approximately equal. Current production is 13 Mbpd of oil and 2 Mbpd of NGL. Average water cut is 90% and average GOR is 20,000 scf/stb. To date, 128 wells, including 24 sidetracks have been drilled. Currently 56 producers and 26 injectors are active.

Calcite Dissolution Behaviour During Low Salinity Water Flooding in Carbonate Rock

“…In this way oil sticks to the clay. [Seccombe et al 2008]. LSF recovery mechanisms, like the expansion of the electric double layer (EDL) and ion exchange, can break these bonds and the oil will be mobilized [Lager et al 2006].…”

“…Initially, the sandstone rock surface is intermediate wet. The remaining oil saturation after the high salinity waterflood was 41% and after the low salinity waterflood, 27% of the oil remained in the reservoir [Seccombe et al 2008]. These values were based on a single well chemical tracer test (SWCTT).…”

Tracer monitoring of enhanced oil recovery projects

“…It exploits the difference in travel time between injected ester and alcohol generated in-situ by hydrolysis and was pioneered in the US about 40 years ago by Esso [10,11]. SWCTTs have been used to identify enhanced oil recovery (EOR) potential as well as to evaluate the effect of EOR in numerous on-shore fields [12] and some off-shore locations [13][14][15]. Recently there has been a growing interest in injection of low-salinity water to reduce remaining oil saturation and enhance oil production.…”

“…Recently there has been a growing interest in injection of low-salinity water to reduce remaining oil saturation and enhance oil production. Several pilot tests have been conducted and the SWCTT is used in these projects to measure oil-saturation prior to and after the low-salinity water injection [13][14][15][16]. On the Norwegian continental shelf two pilot-tests have been conducted recently, in the Snorre-field [15] and in the Heidrun-field.…”

New mobility ratio definition for estimating volumetric sweep efficiency of low salinity water injection

“…18 Two pore volumes basis of LSWI is recommended for optimum oil recovery. 19 2 1 27 Keywords: 28 Low salinity water injection (LSWI) 29 Improved estimation of volumetric sweep 30 efficiency 31 New mobility ratio definition 32 Fractional flow and tracer methods 33 LSWI effect on displacement and volumetric 34 sweep efficiencies 35 3 6 a b s t r a c t 37 This paper investigates the effect of low salinity water injection (LSWI) on both oil displacement and vol-38 umetric sweep efficiencies.…”