In shale plays where horizontal wells are often required to achieve profitability, a common industry practice is to start evaluation of a prospect by drilling vertical or low-angle wells. Extensive formation evaluation measurements, which are then used as points of reference are then run. Interpretation data acquired from vertical wells is used to describe the local reservoir and determine horizontal well placement objectives. Horizon depths may be adjusted for depth based on surface seismic or observations from other wells, otherwise formation properties in the horizontal are considered to be invariant. Acquiring formation evaluation measurements along the lateral is often considered to provide little additional value, are not worth the extra rig time, risk, additional cost, and difficulties associated with tool conveyance. These wellbores typically will be stimulated to test production or converted to a horizontal well via sidetracking.
Horizontal wells are commonly steered using simple gamma-ray measurements correlated with the vertical pilot wells. Detailed examination has revealed that steering results for horizontal wells, using averaged gamma ray correlation techniques and subsequent structural modeling, yield non-unique solutions. This may result in less than optimum reservoir exposure over the drilled interval. With the integration of Logging While Drilling (LWD) technology into the Bottom Hole Assembly (BHA), real-time formation evaluation measurements provide key information for detailed rock property assessment across the target structure, consistent with pilot or offset well evaluation methods, and facilitate accurate well placement. Additionally, real-time and pseudo real-time LWD measurements have been successfully used for hazard avoidance, enhanced penetration rates reducing drilling time, and most importantly completion design optimization. While the LWD method offers some appreciation for the inconsistent rock quality and variable production results across wells, it also provides conclusive insight into the reservoir-production relationship. Understanding of this relationship provides for target refinement within the reservoir column and an optimized completion for an overall increase in reserve recovery.
This paper investigates the use of gamma ray-only measurements only for evaluation and geosteering, and then details the geosteering application using more robust formation evaluation and the subsequent completion optimization. Results are verified using micro-seismic monitoring and production data within a shale gas play. In this manner, structural models, formation evaluation and completion designs are combined to form the technological foundation that can unlock the secrets for viable and sustainable shale gas development.