For tight or unconventional reservoirs, multistage horizontal well fracturing and completion are necessary and important parts of the development. Previous studies have demonstrated that an engineered completion design improves lateral coverage and productive reservoir performance as compared with purely geometric designs. Because engineered completion design focuses on completion aspects, we introduce the idea and a case study of using geology quality (GQ) to improve multistage fracturing design in horizontal laterals. Reservoir Quality (RQ) and Completion Quality (CQ) are often based on formation evaluation result, capturing lithology, porosity, resistivity, or geomechanical properties only a few inches or feet from the wellbore. However, hydraulic fractures penetrate tens to hundreds of feet vertically and hundreds of feet horizontally. Therefore, geological factors must be considered to account for reservoir variability on a larger scale.
There are logical engineering reasons to vary the fracturing design along the lateral between stages. For a lateral that lands in the target reservoir, the fracturing design should be based not only on average reservoir properties but also reservoir height. For a lateral that lands above or below the target reservoir, special considerations must be taken to evaluate the chance that fractures will propagate into the target reservoir.
In our work, we convert this geology consideration quantitatively into a geology quality (GQ) number. This number reflects the reservoir effective height and relative distance from the wellbore, so that the fracturing design can be optimized in each stage along a horizontal lateral.
In a case study from Sulige Field, central China, we integrated GQ into six horizontal fracturing designs and operations with positive results. Breakdown issues were eliminated during the operation, and the production result satisfied expectations. Subsequent production analysis revealed the true contribution from different sand and shale sections in the lateral, enabling positive correlation to the GQ definition in the well. The addition of GQ to RQ and CQ has improved the science of optimizing fracturing design, completion staging, and perforation schemes.