Role of sulphates and chloride ions in improved oil recovery in a hybrid smart-low salinity flooding technique

Al-otaibi, A

Abstract

The growing demand for energy to cater for the growing world population has forced the exploitation and utilisation of existing hydrocarbon resources. Oil and gas are deemed the most conventional and common sources of energy, formed as a result of degradation of fossils deeply buried in underground. Utilising oil and gas require their extraction from their “traps” termed reservoirs. Their production is possible through the natural energy (in form of pressure) which forces the resources to the surface. The oil production from the well will eventually decline steadily due to pressure depletion associated with it and production will be halted. Studies have shown that almost 300 billion barrels of oil remain untapped to this day. This has forced the innovation and investigation of efficient recovery methods to recovery additional oil, and to reduce the residual oil saturation from the reservoirs. There are several methods employed for enhanced oil recovery (EOR). The choice of each method is peculiar to its application, ranging from demographic to economical vices. However, a method of EOR that shows a potential in terms of versatility and wide scale applicability is Low salinity flooding, which is characterised by many mechanisms including fine migration, electrical double layer expansion, multivalent ionic exchange, and micro dispersion. Despite much research on theses mechanisms, sulphate ions facilitate the fine migration at low concentration, while presence of chloride promotes micro dispersion. This study for the first time utilised a combined engineered water of sulphate and chlorides ions to understand its suitability for sandstone reservoir of Wara field, which has undergone successfully secondary recovery, with low salinity EOR being a candidate option for the tertiary recovery. Low salinity flooding as a method of enhanced oil recovery has been proven to provide the additional oil recovery from the reservoirs. It is cheaper and more efficient method compared to the cheapest conventional EOR technique (CO2 flooding). This study aims to investigate the feasibility of using low salinity flooding using engineering smart water through laboratory experiments on different real sandstone core samples obtained from the reservoir. A mineralogical analysis to obtain the rock composition, particularly clay types, was carried out using a combination of EDX, XRD, and SEM techniques. This will help to establish the fluid rock interaction in the subsequent analysis. Furthermore, a core flooding process was carried out, at reservoir conditions of 1600 psig and 40 °C, to investigate the effect of salinity variation and composition on the displacement efficiency and also to evaluate the dominant displacement mechanism of the process for this application at these conditions. From the mineralogical analysis, Kaolinite clay was present in the core samples from the characterisation techniques aforementioned. This is an important finding as, stated in a number of literatures; it is a type of clay that is susceptible to the effects of low salinity by being a non-swelling clay which is responsible for some of the proposed low salinity displacement mechanisms. This is the first step which will provide information on the low salinity water formulation in order to have compatibility with the formation of interest and also an efficient medium through which additional oil recovery will be realised. Additionally, the results from the core flooding process indicated that the displacement by sulphate-based salts yielded the best recovery factors compared to the chloride-based brines. This is as a result of the interaction between the rock surface and the anionic components of the injected low salinity brine. A proposed mechanism showcased the role of ionic brine components in the wettability alteration associated with improved oil recovery. Furthermore, IFT reduction was also realised and contributed to the substantial recovery by the SO4 brine. another noteworthy finding is the conformance effect which will affect the displacement front and impeded vertical sweep across the pay zone during EOR.

Citation

Al-otaibi, A. (2021). Role of sulphates and chloride ions in improved oil recovery in a hybrid smart-low salinity flooding technique. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Nov 9, 2021
• Publicly Available Date: Oct 14, 2023
• Award Date: Oct 13, 2021