Cotton Valley tight gas sands in the east Texas Basin of North America consist of very fine-grained, well-sorted quartz arenites and subarkoses that are overprinted by significant diagenetic processes. Stratigraphic variations in rock type control gas production. Hydraulic fracturing delivers economic gas production.

Recently, horizontal wells over 4,000 ft long consisting of more than twelve hydraulic fracturing stages have been drilled. The good gas producing rock type reservoirs are usually less than 14 ft thick and exhibit strong diagenetic overprint. Low gas prices challenge the use of sophisticated geosteering logs. Using a very basic Gamma Ray (GR) log and very limited offset pilot well data, chasing such thin and variable sand bodies over a distance of 4,000 ft in a marginal marine sedimentary environment is daunting. Apart from this, horizontal wells that target thin layers present unique challenges to completion optimization.

Quad-combo log data, including azimuthal density image data, was acquired using a Logging While Drilling (LWD) tool. Extensive log modelling was performed by combining the horizontal well logs with logs from its two offset vertical wells, and consistent interpretation was achieved. Log modelling has helped the post-drill well diagnosis in geosteering, completion design, and production performance. It has also supported formation evaluation.

This paper will highlight an integrated study workflow in tight gas sands using open-hole and cased-hole data. It will demonstrate the geosteering challenges, explain the log modelling process, and display the formation evaluation results. Geomechanical study, together with hydraulic fracturing data and production log data will be used to confirm that good gas producing rock types are easier to fracture, and they contribute better to production.

You can access this article if you purchase or spend a download.