LWD for Well Placement and Formation Evaluation Towards Completion Optimization in Shale Plays

Abstract

Abstract Unconventional shale plays are characterized as low porosity and low matrix permeability reservoirs. In addition, they lack an obvious seal or trap, are of large regional extent, and understood to be heterogeneous in nature. Due to this understanding, vertical, pilot wells are commonly drilled to evaluate rock properties and determine horizontal shale gas targets. Horizontal wells are drilled then completed by means of hydraulic fracturing to maximize reservoir contact and enhance production performance. To position the lateral production borehole within the defined target, geosteering is commonly performed using a single averaged gamma ray measurement. In the initial development phases, this is often perceived as the most economic means for measuring and steering the production hole. However, acquisition of sufficient LWD data demonstrates that by relying on a single measurement, structural models can be made to present several different possible correlation scenarios. Obviously, a non conclusive structural interpretation will negatively impact any efforts of evaluations for efficient field development. While, averaged resistivity measurements may be utilized as an additional correlation reference to complement gamma ray, improvements to correlation accuracy are best achieved with azimuthal images such as density, resistivity or gamma ray images. Real-time image measurements are used identify thin layers while cutting up or down dip as well as structural dip authentication along the well trajectory to provide a high level of confidence in the interpreted geosteering model. Effectively, an accurate structural model is also an effective tool to design completion, correlate formation properties and refine target sizing while providing the foundation for formation evaluations. This paper illustrates how correlations using only an averaged gamma ray measurement for structural modeling and steering of a production hole can result in multiple interpretations. This uncertainty is a potential cause of inconsistent reservoir interpretations and low or varied production across a given field. In comparison, acquiring sufficient measurements while drilling for formation evaluation, and well placement can be applied to deliver consistent production results and provide a common platform for completion design practices.