Production in shale is highly related to the well placement in both sweetspot and fracable zone. Due to both, market conditions and also shale property, geosteering in tight shale reservoirs have generally employed basic and economical steering tools, such as gamma ray; however, though the tool provides some data to steer the well, the data provided does not allow for predictions of fracability and production potential of the shale rock. This paper introduces a new geosteering approach, which augments existing techniques by providing data to also help well placement, then design stage and perforation location. This novel formation evaluation technique is essentially building a quantitative model of "sweetspot fracable window" for shale, which can help to land and target most prospective zones. The main quantitative data is obtained through measurement of cuttings samples at well-site in semi-realtime on a field portable SEM (Ashton et. al., 2013), generating the mineralogical and elemental composition of the samples, and also providing rock textural data. Although cuttings are evaluated after the well being drilled, cuttings are only physical representative rock samples from the bottom of the hole.
Case studies presented in the paper have shown that maintaining the well path in the sweetspot fracable window can result in better well production after fracturing. Thus, the goal for geosteering is to ensure as much as possible that the horizontal well trajectory is maintained within this window. Additionally, the cuttings data generated during the drilling process can also be used both during and after TD to generate optimized completion design, aiming to further maximize well productivity. The cases’ study in this paper also shows that, compared with conventional wireline logging data, the on-location cutting based analysis is able to generate richer mineralogical and elemental data throughout lateral wells, providing a better understanding of geological heterogeneity. Meanwhile, the authors also apply several strategies to calibrate the cutting depths and cuttings’ time lags.
The authors created an approach, which can provide a fast analysis for enhanced reservoir navigation, to keep the well trajectory within a predefined sweetspot fracable zone. The production analysis of the wells, hereafter, verifies that the higher the rate of intersecting into sweetspot fracable zone, the higher production the well receives. This approach then assists in generating cost-effective completion optimization of stage placement and perforation, with the ultimate goal of increasing the investment returns.
In conclusion, the production statistics of the wells verifies the higher rate of intersecting into sweetspot fracable zone, the higher production the well receives. The goal for geosteering is to ensure as much as possible that the horizontal well trajectory is maintained within this window.