Fluid determination in in-situ condition is extremely desirable to understand hydrocarbon potential of Jurassic unconventional reservoirs in West Kuwait (WK). Conventional coring methods typically lack the capability to determine in-situ conditions of a reservoir once the core sample is recovered and transported to the laboratory. Due to the change in pressure and temperature throughout the recovery process as well as the associated subsequent on-site handling procedures, a significant amount of oil / water and especially gas will be lost or significantly altered. Pressurized coring or pressure-retained coring methods can mitigate or potentially eradicate these shortcomings by encapsulating the core sample downhole, thus preventing these disadvantageous effects and preserving the core sample as close to its in-situ conditions as technically possible. However, due to scarcity of established pressure coring systems or services in the market, and especially for the harsh reservoir conditions in Najmah (NJ) Kerogen (>14,500 ftss; >14,000 psi; 250°-260° F), no best practice is in place to recover and analyze pressure retained core samples in the oil and gas sector. This paper aims to describe the great achievement of a newly developed method of pressurized coring and its enormous benefits with regards unlocking unprecedented options in fluid analysis of NJ Kerogen. This new integrated approach allows for improved insights by measuring accurate rock & fluid properties close to pristine reservoir conditions.
Najmah Kerogen is the key source rock in West Kuwait. It is part of Najmah-Sargelu formation that deposited in Middle Jurassic, mainly in the outer ramp to basinal environment under restricted and intermittent anoxic conditions. The Kerogen formation mainly comprises of calcite, dolomite, quartz, kaolinite, pyrite, and kerogen. It is sub-divided into three layers in which the middle argillaceous limestone layer is packed between two organic-rich layers. Recent study of unconventional reservoir characterization has identified the world-class hydrocarbon potential of Kerogen in Kra Al-Maru (KM) field (Nguyen et al. 2022). The field is defined as a four-way closure with NW-SE trend, located in the west of Kuwait. In total, eight wells have been drilled to develop Sargelu limestone reservoir including recently drilled Well-A & Well-B (Fig. 1). The secondary objective of these two new wells was to acquire fully retained pressurized cores in Najmah Kerogen in order to obtain accurate rock & fluid properties close to pristine reservoir conditions. This is because fluid determination in in-situ condition is extremely desirable to precisely evaluate HC potential of Kerogen since there are numerous challenges, especially the factors of reservoir pressure & depth. In traditional coring jobs, a significant amount of gas is not captured (lost gas) when the core is surfaced. Moreover, the fluid composition is also drastically changed. The implementation of pressurized coring jobs in Well-A & Well-B aimed to solve the above-mentioned issues.