Characterization of the lateral heterogeneity of reservoir properties is an important consideration during the design of horizontal completion operations in unconventional plays. Traditional geometric designs do not differentiate adjoining rocks based on lateral heterogeneity. This paper presents an academic case study from the Eagle Ford shale play in which the authors analyze and validate an engineering design using observations from an operator's completion design-based fracturing operation. The paper also proposes a low-cost, low-risk solution workflow for these unconventional reservoirs.
An unbiased and repeatable fracture stage and perforation cluster optimization program was used for the engineered design. The input for the engineered design originated from a two-dimensional (2D) petrophysical and geomechanical model. This model was constructed using correlative property modeling that used openhole (OH) logs from an offset vertical well and a calibrated casedhole (CH) pulsed neutron log (PNL) that was acquired in the lateral. A conventional OH logging suite was also run in the same lateral, which was compared to the calibrated log data as a part of the validation process.
The resultant 2D property model provided an appropriate representation of the subsurface reservoir properties. Lateral variations of those properties were duly addressed by optimizing the fracture stage and perforation clusters. This workflow also accounted for the relative position of the wellbore, with respect to the stratigraphic and the reservoir boundaries, as predicted by the 2D property model. During execution of the operator's completion design, reservoir properties were carefully observed and compared with those predicted by the 2D property model and the engineered design derived from the same. These observations validated the properties and justified the optimizations in the completions program and the modifications necessary. For example, a number of stages during the stimulation treatment were initially unsuccessful, thus allowing less than 10% of the total designed proppant to be pumped. During evaluation of the post-stimulation results, it was observed that these zones were identified as less promising by the 2D property model-derived engineered design because of unfavorable reservoir properties. The engineered design model recommended not completing these zones.
The observations from this study showed that completion operations in a long lateral should be designed to account for the lateral variability of the reservoir. The engineered completion design optimized hydraulic fracture stages and perforation clusters based on the petrophysical similarity and merits of the adjoining sections. The methods presented helped mitigate risk and supported rigless operations for characterization in a cost-sensitive environment, thus reducing the costs and effects of hydraulic fracturing operations.