Integration of Diagenetic Rock Typing with Advanced Geophysical Attributes for Well Placement Optimization in Underbalanced Coiled Tubing Drilling

Abstract Underbalanced Coiled Tubing Drilling (UBCTD), which is the practice of drilling in a wellbore pressure that lower than the formation static pressure to allow the well to flow while drilling, became a common practice in Saudi Arabia in recent years due to its ability to significantly enhance wells performance in terms of production and drilling efficiency. However, common drawbacks of this technique are the lack of real time data due to the slim hole size as it only captures the gamma-ray and gas rate while drilling, and it is highly affected by the subsurface heterogeneities and diagenesis of the targeted reservoir such as clay precipitations and facies changes. Therefore, optimum well placement is required to improve well results which can be achieved through integration of different techniques such as Diagenetic Rock Typing and advanced geophysical attributes such as Mono-frequency, RMS-amplitude and acoustic impedance. Diagenetic Rock Typing is a technique which separates the reservoir into different rock types based on core, log, and petrographic analysis of the clastic reservoir in which the best rock type shows the least amount of total clay content, typically less than 5%, and highest effective porosity, commonly more than 5%. These rock types can be propagated into a 3D domain by applying geostatistical techniques to map subsurface heterogeneities. Integration of this techniques with other geophysical attributes including Mono-frequency, which is a technique used to identify gas sweet spots by separating the seismic volume into different frequency bands, results in generating a map that supports optimum placement for UBCTD wells. The feasibility of this techniques was tested in a clastic reservoir. The reservoir is known for its heterogeneity and sever diagenetic processes such as clay precipitation, quartz cementation, and quartz overgrowth. An anomaly was identified in field "A" in an area where there is minimal wells penetration. The anomaly was identified as a potential gas bearing reservoir using Diagenetic Rock Typing, Mono-frequency with other seismic attributes including RMS amplitudes. Two UBCTD wells, ‘Well-1’ and ‘Well-2’, were drilled targeting the sweet spot shown in the various maps, and produced exceptional results. Further UBCTD operations can be enhanced, in terms of production and economic feasibility, using similar approaches through integration of different reservoir characterization solutions.