Spiral Hole Moderation Enhances High-Resolution Borehole Image Interpretation Across Fractured Carbonate Reservoirs

Abstract

Abstract Dynamic phenomena while drilling such as borehole spiraling or corkscrewing can create a physical imprint on the borehole surface, which mask fine features of imaging. During a drilling campaign in a carbonate reservoir using logging-while-drilling technology, corkscrewing was severely impacting the ultrahigh-resolution borehole image quality. As a result, fracture identification was affected that had significant implication on reservoir characterization, description, and hydrocarbon recovery strategies. Consequently, a collaborative project was initiated to find a solution to overcome these phenomena. The impacted wells in the field and other nearby fields with similar formation characteristics were analyzed at first to find commonalities. Based on this investigation, a suggested solution to eradicate the spiraling was to reduce the interaction forces and minimize the adverse effect on the directional drilling capacity of the bottomhole assembly (BHA). A new bit design was required with design elements expected to mitigate or minimize borehole spiraling. With it, the bit gauge length was increased as well in successive wells combined with drilling parameter optimization. Drill bits from several vendors were used to study the impact of different bit designs. The results from the detailed technical investigation indicated that borehole spiraling resulted from the bit-to-formation interaction. The testing of different bit gauge lengths and shapes was aimed at reducing the bit-to-formation interaction. On the other hand, the new bit design assessment raised another challenge, which was the BHA steerability and control. An increase in gauge length was expected to reduce the spiraling but potentially impact the steering capability negatively while drilling the well. Hence, a thorough design of the bit and BHA was performed to ensure the well steerability would comply with maintaining optimum well placement criteria. Each increase in gauge length minimized the severity of the borehole spiraling effect. The critical factors determined to reduce spiraling were the gauge design and length. Consequently, the borehole image quality obtained was significantly enhanced, enabling detailed fracture identification and reservoir characterization. Additionally, the enhancement in borehole image quality enabled openhole completion to be designed methodically to isolate conductive fractures with aim to extend well life, delay water breakthrough, and as a result maximizing reservoir sweep. This paper presents the methodology and results of the bit design test to mitigate the presence of borehole spiraling. The quality of the ultrahigh-resolution borehole image was significantly improved, which enhanced the confidence in reservoir characterization, fracture modeling, and field development strategies such as completion design.