Abstract
Heterogeneity of properties along horizontal shale gas wells has a significant impact on the quality of completion as well as on production from each stage. This heterogeneity can exist in the quality of the reservoir, such as changes in kerogen content and maturity, free porosity, and water saturation, and it can also be seen in factors which directly affect the course of induced fracturing in the well. These factors can be faults, natural fractures, stress regime changes, etc.
Historically, it has been difficult to map these properties because some of the measurements required logging in openhole environments using wireline tools. Recently, logging-while-drilling and through-casing-logging measurement techniques have been developed to achieve similar results in a safer, more controlled environment.
A large number of horizontal wells have been drilled in gas shales in the USA and Canada. Some of these wells have been logged in an attempt to understand variability. The authors have studied these data sets in detail, and the concepts presented here are based on observations from these data sets. We use a data set acquired in a Canadian shale as an example to illustrate the concepts of property heterogeneity along the laterals. This well is a 1,000-m long lateral which was supposedly drilled in the same, homogeneous rock, yet it shows substantial property differences along its length, suggesting the importance of evaluating horizontal wells.
Once these properties have been mapped, many questions can be raised. Can we increase production from the same horizontal well, which has already been drilled (Potapenki et al SPE 119636; Ketter et al SPE 103232) ? Can we do something better in planning the completion to get more gas out of it? Would it be possible to save a well from geohazards if we knew how we might connect to them? Can we select the optimum perforation interval when we know the quality of cement behind pipe? The answer to each of these questions can result in substantial gains in efficiency and reduction in risk, while providing major production boosts. To determine definitive answers to these questions, production data over time would need to be analyzed. These data were not available at the time of writing this paper; hence, a detailed discussion on the specifics of the correlations between properties and production is left for another paper.
