Abstract
A cost-saving solution is presented herein illustrating how a specialized form of artificial lift can be deployed to accommodate a wide range of production rates, overcome difficult operating circumstances and rapidly test multiple zones with only a single run of downhole equipment.
The operator initially set out to solve this "how to" challenge in Kenya after first discovering oil in 2012. Qualifying and quantifying reserves in this case study required utilizing artificial lift systems in unconventional completions for conducting both DST's (Drill Stem Tests) and EWT's (Extended Well Tests). Conducting DST's are often costly as completions rigs are utilized to run and remove artificial lift equipment. The operator tested several different lift methods during earlier DST's and concluded that subsequent DST's and EWT's would likely utilize only one lift method, for multiple reasons.
Oil and Gas exploration in remote places such as Kenya has inherently high costs due to complex logistics and unknown reservoir characteristics. The first challenge was how to test multiple zones with minimal rig activity. The second challenge was selecting a combination of surface and subsurface equipment capable of accommodating a wide range of reservoir fluid compositions, zonal flow characteristics and operating temperatures, throughout isolated tests for each zone.
Northern Kenya's oil, with an API gravity of 31 – 38° API has a high wax content of 24-37% and a variable gas-oil ratio of 70-250 SCF/Bbl. Furthermore, wax appearance temperature (130-141 F) and the temperature gradient of these wells (18 °F/1000 ft.) and reservoir temperatures of 165-212 F, dictated the oil must be either heated or chemically treated, to assure flow to surface during tests.
Several zones demonstrated ability to flow naturally and were thusly killed during completions for a safe working environment. Accordingly, removal of kill fluid from the wells required some form of artificial lift to clear the way for flowing-well tests. However, it was deemed any AL system must perform all tasks without physical disturbance of equipment, to allow the well to transition smoothly from being artificially lifted, to flowing freely and back again after tests commenced, nor could the AL system impede flowing characteristics as any disturbances or disruptions could skew test results via interruption of data-collection continuity. Multiple tested zones in the same well bore demonstrated a wide range of Productivity Indexes (PI) which required AL equipment be compatible with low to moderately high (<50 to 1000+) BPD rates, high Gas Oil Ratios and because of the high wax content, inclusion of flow assurance measures (downhole heaters) mandated the AL system be compatible with a wide temperature range.
The unique solutions deployed in East Africa on multiple wells to address real-world issues met all of the challenges and dramatically improved testing turnaround time for each well, yielding a much more economically-efficient model for future exploration endeavors.
