--> --> Geological Focused Data Review Accurately Describes Production Factors in Mature Reservoir

AAPG Southwest Section Annual Convention

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Geological Focused Data Review Accurately Describes Production Factors in Mature Reservoir

Abstract

Horizontal wells present unique, complex problems. The horizontal well bore can traverse multiple depositional sequences and can cross many depositional facies with variable geomechanical and poro-perm properties in a single well. These geological boundaries can change the production potential and impact the well’s commerciality. Unforeseen localized variations in structure or rock fabric do occur and can hurt program economics if well performance is poorer than expected. In this project, geosteering services were discontinued because a well-defined understanding of the reservoir had already been established. Regional and local dip information were well known and the impact on both drilling, evaluation, and production had been consistent. The problem became apparent in a horizontal well drilled between two legacy vertical fields. It was deemed to be a modest step out and low risk. Midway through the lateral, the gas and cutting shows diminished abruptly. It was assumed that the pre-drill structural interpretation was in error and that the lateral had traversed up dip back into tighter top seal rock. Attempts to change bit inclination were successful but did little to migrate the well bore into productive reservoir. Gas shows and cutting shows were never recovered. Upon completion, over half of the lateral footage had to be abandoned due to water production. Re-steering to verify the well path within the geological structure and section was applied to the available information. This was an attempt to track the actual path of the well in the reservoir and to identify the different reservoir sections that were encountered in the drilling process. After several iterations, a geologically complex model was derived that matched all of the available drilling and mud log information and corresponded to actual production results. Re-steering added reservoir knowledge to this well- developed drilling program by illustrating the variable nature of localized structure and reservoir quality that could not be anticipated from offsetting well data. A key insight was the need to have a geological description process in real-time. Geosteering was added on all subsequent wells as a critical geotechnical assessment component. This helped keep active well bores in the most productive and economic parts of the reservoir.