Fluid Mapping-While-Drilling De-Risks Reservoir and Fluid Data Acquisition Workflow in a Brown Field
Authors: Abdul Wahab Norsharmila , Suhaimi Muhammad Haniff , Antuni Aryanore Nafarine , W Aziz W Nor Afiqah , Mohiyaddin Muhammad Zaki , Garcia Mayans Aldrick , Haq Shahid Azizul 
Published: June 2021

Located offshore Malaysia, Field A is a highly complex elongated anticlinal structure with hundreds of faults. It includes over 70 hydrocarbon bearing sands deposited in a lower coastal plain environment. Producing since the late 1970s, Field A has gone through several asset rejuvenation plans. The latest one aimed at appraising and draining several untapped fault blocks. Although no major surprises were expected in terms of lithologies, uncertainties remained on fluids’ nature in multiple sands and on the possible isolation of the fault blocks. This paper illustrates how an operating company introduced a new while-drilling downhole formation fluid data acquisition workflow to successfully de-risk and address these challenges.

Conventional formation evaluation is challenging in these fluvial environments, as it includes laminated reservoir, variable permeability, and presence of light, potentially saturated, hydrocarbons. Lessons learned from the previous rejuvenation campaign highlighted the importance of formation testing and downhole fluid analysis (DFA). The planned campaign required drilling two complex 3D profile wells (80-degree tangent followed by 35-degree drop through the targets). Pre-drill discussion raised various concerns: potential well control issues due to pumping light hydrocarbons in the borehole; sticking risk due to complex well trajectory and potential depletion; in-situ evaluation of CO2 for well deliverability analysis; and the number of logging runs, wiper, and post-drilling cleaning trips. In addition, the financial constraints on infill development called for the need of early, real-time enabled decisions for perforation and completion optimization.

The selected drilling bottomhole assembly consisted of an integrated multi-physics logging-while-drilling toolstring including fluid mapping-while-drilling (FMWD) technology to de-risk the fluid acquisition program. The integration of pressures and DFA measurements with petrophysical data helped to identify and understand the distribution of fluids and fault blocks connectivity. The campaign proved to be very successful. All sand horizons were pressure tested, providing a fluid pressure profile description yielding gradients where applicable, differential pressure estimation, and connectivity information. The uncertainty associated with petrophysical fluid identification was addressed, and the use of FMWD showed no free gas in the tested zones. Fault block isolation was proven. Reservoir fluid and mobility profiling helped to optimize the well perforation and completion strategy and assess the producibility of the wells. The acquisition sequence was safely performed in one trip from bottom to top with no overpull observed. No wiper or post-drilling cleaning trips were required due to continuous mud circulation during data acquisition.

This paper describes how this operating company successfully introduced a new while-drilling downhole formation fluid data acquisition workflow in a brown field. The workflow positively impacted the field development decisions. The FMWD de-risked data gathering operation under tight economical constraints and addressed formation evaluation and drilling and completion challenges during the evaluation of untapped blocks in Field A.