Fracture Conductivity Calculation Using Mass Balance, Modeling, and Well Performance Data in Saudi Arabian Deep Gas Reservoirs

Abstract

Abstract The fracture conductivity values reported from the laboratory tests are based on ideal conditions and are usually higher than what actually contributes to production. In reality, the conductivity values are impaired by numerous factors in the reservoir such as high unconfined compressive strength, condensate dropout, proppant embedment, gel damage, etc., and cannot be fully captured in the laboratory measurements. The software models used by the industry to calculate fracture conductivity are specific to certain reservoirs, formations, and/or laboratory conditions and cannot be extrapolated or used for all reservoirs. In this paper, a workflow has been presented to compute fracture conductivity using various techniques and compare them to see what matches closest to reality in terms of well deliverability. First, fracture geometry and conductivity is computed using a mass balance and pressure match. Second, fracture conductivity is computed from the Cinco-Ley correlation and using industry software to estimate at static and dynamic well conditions using closure pressure, actual well performance, and bottomhole flowing pressure measurements. A range of fracture conductivity is computed during initial and later production periods by matching well rate and pressure behavior data. The calculations show the fracture conductivity achieved after a fracture treatment for specific reservoir conditions and how the values change during the production life of a well. Later, correlations relating to productivity increases with reservoir rock and pumping properties are used to optimize fracture treatments such that high rates can be achieved and sustained. The paper also presents different fracturing properties as functions of well productivity that can serve as guidelines for improved application of fracturing technology. Fracture conductivity is one of the most important parameters that impact post-fracture sustained production. Regardless of the formation permeability, higher conductivity values always assist in quicker fracture fluid cleanup and enhanced rate. There are a number of factors that affect the ultimate conductivity achieved in a fracture. They include fracture fluid gel and cross-linker loading, type and size of the proppant, proppant stages, concentration, and pumping sequence, and post-frac fluid cleanup efficiency. Introduction Hydraulic fracturing is being used in the Pre-Khuff sandstone reservoirs in Saudi Arabia to achieve higher sustained gas production and sand control in Saudi Arabian gas reservoirs1. The variability in reservoir properties in Pre-Khuff is significant with some areas that are extremely prolific where sanding becomes a major challenge with slight pressure drawdown while other areas that are tight with high compressive strength required long condictive fractures for commercial production.