After more than a decade of producing oil from the thick marine sand reservoirs in the HaDeXun oil field in the Tarim basin of western China, focus has shifted to the challenges of drilling thinly laminated reservoirs. To maximize efficiency and production, geosteering services, as well as bottomhole assembly (BHA) and bit optimization, were used for the successful drilling of two thin sands, which resulted in reservoir contact of 100 and 96%, respectively.

This paper presents a case study discussing prewell modeling, the planning process, execution, and results of drilling two complex thinly laminated reservoirs in a single well within a mature field. Each less than a meter thick, the thin reservoir targets are located above the main DongHeSha (DHS) sand reservoir and are bound by shale with uncertain formation dips. Adding to the complexity, the thin sands have limited lateral extension; however, recent improvements to well-placement technology have enabled these reserves to be recovered, which was almost impossible with previous conventional directional drilling methods.

An advanced well-placement process is discussed in the paper using azimuthal at-bit-gamma images and inclination measurements positioned only 1 m from the bit, a point-the-bit rotary steerable system, and modeling software for rapid, accurate data interpretation and pre-emptive wellbore positioning. Collaboration across teams resulted in an optimized BHA, which enabled directional changes to be made during the landing process to accommodate geosteering interpretations that refined the geological model to reduce uncertainties associated with the location of the reservoir top and bounding formation dips. Once landed, the well was successfully steered within the two thin sands, delivering one 303-m lateral section with 100% exposure to the reservoir and a second 300-m lateral section with 96% sand exposure.

This paper presents a practical workflow encompassing the integration of all available data, including seismic, offset-well petrophysical logs, mud logging, and real-time logging-while-drilling (LWD) images to overcome dip uncertainty and maintain the wellbore within the thinly laminated target sands. Also presented is a customized design of the BHA and drill bit, which were necessary during the landing portion of the drilling program and, when used together, helped reduce vibration, increase the rate of penetration (ROP), and enhance dogleg building capability to maximize reservoir exposure in a safe and efficient manner.

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