An Integrated Holistic Well Productivity Improvement (WPI) Approach: Infill Wells of an Offshore Oilfield Experiencing Unexpected Declining Production
Authors: Choi Joel , Manning Nickolas David , Carvajal Valdez Lourdes Ivonne , Razmgar Kourosh , Manning David Keith , Dabiri Mehdi , Weathers Gordon , Saeedi Ali , Guillory Ryan Scott , Bin Salleh Fairus Azwardy 
Published: October 2022

This paper discusses the integrated approach for investigating the declining production rates in an offshore Basin located in Western Balingian province, Malaysia. Four infill wells drilled in 2017 have suffered formation damage that has severely limited production rates. Re-perforation and stimulation attempts have resulted in some improvement, but the problem of declining production rates persisted.

The work was conducted in two phases. Phase-1 focussed on understanding the damage mechanisms associated with existing wells. Testing the existing Reservoir Drill-In Fluid (RDIF) with static Permeability Plugging Apparatus (PPA) and dynamic Wellbore Conditioning Test (WCT) with reservoir core plug samples allowed for a base case result. The RDIF, and more specifically bridging package, was then optimised via static and dynamic testing to include sized calcium carbonate with reduced barite loading to reduce filter cake invasion. During dynamic testing, it was apparent that critical velocity or kaolinite fines migration was another contributing factor to the formation damage. It was proposed at the end of this phase that critical velocity testing be conducted to further understand and target the problem. As all previous reservoir core plug material had been exhausted or were unsuitable for testing, it was recommended that freshly cut cores be used in the next phase of testing. Furthermore, if the core material was of initial, non-produced state without the influence of production fluid flow on the reservoir matrix, it would allow for significant information to investigate the declining production rates as well as increasing well productivity.

The ensuing six well drilling campaign utilised the optimised RDIF from Phase-1. One well drilled with the optimised fluid acquired 27 Rotary Side-Wall Cores (RSWC) with no flowback production conducted on the well, ensuring that core plugs were in a virgin state post drilling. Scanning electron microscopy (SEM) of freshly cut RSWC plugs confirmed the RDIF used having minimal filter cake invasion in the new wells. This result was in-line with the results from the laboratory, providing a benchmark for the fluid system in the field.

Phase-2 of the study utilised the RSWC plugs in investigating critical velocity rates of different reservoir sections within the offshore field. Testing involved scaled down-hole production rates with reservoir-matched production fluid viscosity and monitoring differential pressure across a core plug. Critical velocity events were confirmed in the laboratory testing and the results were upscaled for individual reservoir units in the field. Well unloading rates were applied in the field and significant improvement in well productivity was observed. This paper ultimately highlights the importance of exploring the integrated "results matter" approach to analyse the contributing damage mechanisms and discovering solutions for well productivity.