High-Angle Multifractured Completion System Develops Deepwater Subsea Wells

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220794, “Development and Qualification of a High-Angle Multifractured Completion System for Deepwater Subsea Wells,” by Sanjay Vitthal, SPE, Aykut Goncu, SPE, and Victoria Spencer, Shell, et al. The paper has not been peer reviewed. _ Significant volumes of hydrocarbons have been discovered in Upper and Lower Wilcox reservoirs in the Gulf of Mexico (GOM), typically consisting of stacked sets of lower-permeability sandstones. Several of these discoveries have been developed successfully using cased-hole vertical wells and single-trip multizone frac-pack completion systems. The complete paper describes an alternative lower-completion concept for developing these reservoirs referred to as high-angle multifractured (HAMF) well design. The value of the HAMF concept was assessed with reservoir modeling to understand its value for low-mobility reservoirs. Introduction A key feature of these low-mobility Wilcox reservoirs is that they often consist of multiple stacked sets of individual sand bodies rather than only a single-sand, high-mobility reservoir. The initial rate and estimated ultimate recovery (EUR) of any single sand package is too low to justify the cost of a deepwater well. Economics require that each well must combine production from several sand packages. These wells are currently completed using specialized completion systems that sequentially frac-pack each layer using a single-trip tool. While these systems have been successful, they face challenges including high cost; limits to the number of stages; a relatively high minimum distance between intervals; and, often, a fixed perforated interval length for any stage. For reservoirs with smaller hydrocarbon columns, lower mobility, or a limited number of layers that can be commingled with a near-vertical well, EUR and recovery factors (RFs) often are insufficient to justify commercial development. A need exists for an alternative completion concept to unlock these reservoirs. Ideally, the concept should increase the EUR/RF over hydraulically fractured vertical wells without increasing field capital expenditure (CAPEX) while meeting operational requirements of deepwater wells and production systems. A review was undertaken to identify an alternative solution primarily focused on completion concepts that had been successfully deployed in reservoirs with similar characteristics to Wilcox sands. The review led to the identification of an HAMF well as a possible completion concept for developing large, thinning reservoirs or multiple stacked reservoirs. For the purposes of this work, “high-angle” is defined as greater than 75° in the reservoir section. The high-angle entry enables connecting multiple layers to increase total EUR per well while providing much of the production uplift benefit of a conventional horizontal multifractured well. Understanding HAMF Uplift vs. Vertical Fractured Wells To assess the economic benefit of a HAMF well in deepwater, confidence in the results can be achieved by looking at industry analogs and through multiple modeling techniques. This section of the complete paper provides a discussion of analog studies, a developed analytical model for predicting productivity of multifractured horizontal wells, and a simulation study to predict performance of a highly deviated multiple fractured well. The latter provided several insights.