Deciphering Well Performance of Hydraulically Fractured Tight Gas Wells Through Work-Flow Based Study

Abstract

A common horizontal well completion design, in recent times, in tight gas reservoirs includes the ability to place multiple hydraulic fractures along the length of the wellbore. This practice provides a better drainage pattern and the required flow capacities for the gas to flow making tight gas reservoirs economically viable producers. This is the customary completion practice for clastic rock development, which has shown good results. However, in many cases especially when stepping out in regions beyond the established boundaries, completion design by itself is not sufficient to ensure desired production. The standard protocol to get the best chance of placing the horizontal section in good quality reservoir is to first perform petrophysical evaluation of the preferred pay interval, drill a pilot hole through the potential reservoir section and then place the lateral section in the zone of interest. The pilot hole provides a control point and helps reduce uncertainties in drilling laterally through the target pay zone.This typical completion procedure however does not guarantee identical production even in offset wells. In a conceptual case where two offset wells(A & B) with similar pilot hole petrophysical attributes drilled horizontally in the same maximum horizontal stress direction but in diagonally opposite azimuths produce at widely differing rates. Uncertainties in far-field geology, areal limits, pore pressure distribution, rock property distribution, etc.are well known challenges that can contribute to making well delivery predictions difficult. To help in such situations and better understand the differences in well behavior a detailed workflow based study that includes reservoir characterization, well placement, stimulation design and production history matching is required. The objective of such a study would be to address questions regarding reservoir quality and identifiable "sweet spots," the absence of which could result in poor well performance. The workflow study discussed here is a review of well accepted practices with the objective of highlighting challenges and providing insights into the best and most effective ways to develop complex and highly heterogeneous plays. The workflow loop (Figure 1) is an iterative study process where well performance puts the final seal of approval on the pre-job modeling and executionplanin the well delivery process. In cases where the wells fall below expectations the iterative loop would look for additional information to refine the earlier assumptions. This study considers examples where palynology helped improve geological understanding and played a critical role. The workflow sequence is mapped in this paper.