In the current oil and gas industry, unconventional-reservoir development is largely driven by resource plays, horizontal wells and hydraulic fracturing. More specifically, managing associated uncertainty is an important aspect for cost-effective workflow. We address large uncertainties around perforation cluster efficiency and how we manage it. The application of geometric cluster spacing usually leads to only effectively opening and propping a fraction of the total number of clusters. In order to increase the fraction, we have developed a workflow to take currently-acquired drilling and geological data and apply them to a process for selectively engineering our perforations. This process uses gamma ray, drill cuttings, rate of penetration, mud-log gas shows, and gas chromatography to correlate each foot of the lateral and determine which sections of the lateral are in similar rock or the same stratigraphic interval. While this approach is, in general, not as accurate as that obtained from a full horizontal LWD log suite, it is inexpensive, simple, and allows for more cost-effective completions than the purely geometric method.
Although this simple approach to engineered perforations has been employed extensively, in certain applications we can additionally deploy some advanced techniques to improve perforation selection. For example, recently, the requirement to contact a naturally-fractured limestone interval to enhance productivity in an area with no horizontal wells was challenging for the simple perforation workflow. In order to increase certainty and enhance the productivity of the well, a high-resolution logging while drilling (LWD) resistivity imaging log was recorded in the lateral borehole. By integrating the image log into our engineered perforation design, it was possible to mitigate geo-hazards, enhance the productivity of the well and, most importantly, establish a relationship with fracture networks for future wells.
This paper presents and discusses a case study of using our simple and cost-effective engineered perforations. Each cluster, having similar mineralogy, is selected to be in the most productive in relation to the rest of the clusters in each stage. In addition, the use of an LWD resistivity image log in the lateral allows for the enhancement of our engineered perforation design on an as-needed-basis. The resulting optimized completion in our naturally-fractured limestone reservoir provided excellent production results.
