First Worldwide Implementation of 6-inch Slim Advanced Downhole Formation Tester in Challenging North Kuwait Deep Tight Jurassic Gas
Authors: Abdel-Basset Mohamed , Al-Ajmi Saad , Al-Otaibi Fahad , Al-Azmi Mejbel , Al-Mutawa Majdi , Bloushi Taha , Alajmi Sarah , Ayyad Hazim , Metwally Mahmoud , Kho Djisan , Murat Nohut Omur 
Published: February 2023

The novel 6-inch slim Downhole Formation Tester (DFT) with its advanced Downhole Fluid Analyzer (DFA) sampling tool has been successfully implemented as first time ever worldwide in 6-inch open hole and as first time ever in Kuwait in Jurassic gas deep tight gas Middle Marrat carbonate reservoir. Downhole sampling was always being declined by the drilling team due to differential sticking risks associated with long sampling time using conventional downhole sampling tools in tight reservoirs. This paper will discuss the tool's first successful operation to overcome the formation evaluation and fluid sampling challenges and its immediate added value to subsequent completion and stimulation plan.

The formation evaluation of North Kuwait Jurassic deep tight carbonate reservoirs is challenging due to the uncertainty of conventional log measurements and the oil-based mud filtrate (OBMF) invasion. The induction resistivity logging tool, which is based on formation conductivity, is known to have high uncertainty in this low conductivity environment. Deep oil base mud filtrate invasion is also expected and can be observed by comparing real-time logging while drilling (LWD) resistivity and Wireline (WL) resistivity logs. The deep invasion is caused by the slow mud cake building up due to the low formation permeability. The uncertainty in the water saturation computation is further complicated by the parameter's uncertainty of the water saturation (Sw) equation, i.e., variable cementation factor and the saturation exponent. The determination of free water level or the potential water zones cannot be easily determined from the log interpretation alone. In this case study, the high-definition NMR tool was run to detect the free oil, free water and the OBMF invasion volume by continuous T1-T2 mapping. Formation fluid sampling is also needed to confirm the fluid type to firm up the perforation interval. However, the formation pressure testing and fluid sampling in this field had been cancelled in most of the wells due to the operation risk. Low permeability, which requires longer stationary time and the high differential pressure due to the reservoir depletion need to be addressed properly to avoid the risk of the tool getting stuck.

The slim advanced DFT tool design has smart hardware to enable rapid acquisition and automated capture of representative formation fluids in short time that reduces operational risk in challenging open hole environment. Once the presence of representative fluid has been verified, further analysis can be conducted by extensively profiling fluid properties with a suite of high-precision, high-accuracy measurements. The valves, gauges, and hundreds of other key system components have smart controls that are AI ready and can intercommunicate, enabling downhole automation of complex workflows. This ensures that data can be reliably integrated into the reservoir context in real time for quick, informed decision making.

Many operational challenges were faced and overcome by multidisciplinary team integration. The success and demonstrated added value of first implementation encouraged plans for more implementations across other different assets. The sampling results confirmed mobile water and had immediate added value on the subsequent design of a multistage completion that was installed in the sampled well. The following testing results confirmed mobile water from the sampled interval. Results match the fluids computation by the high-definition Nuclear Magnetic Resonance (NMR) results.

The advanced DFT platform can be a better option in terms of cost and operation time. This option used to be impossible in any tight reservoir until the novel 6-inch slim advanced DFT sampling tool was introduced to the industry.