Hydraulic Fracturing Critical Design Parameters in Unconventional Reservoirs

摘要

Horizontal well drilling and hydraulic fracturing have become the enabling technologies for unconventional reservoir development. From tight gas, to oil and gas-producing shales and coal bed methane, all these resources rely on hydraulic fracturing for its commercial viability. The primary goal of the completion in these ultra-low permeability formations is to provide a conductive path to contact as much rock as possible, through the use of multistage hydraulic fractures along a horizontal lateral. Reservoir contact is optimized by defining the extent of the lateral length, the number of stages to be placed in the lateral, the fracture placement technique and job size. Fracture conductivity is determined by the proppant type and size, fracturing fluid system as well as the placement technique. While most parameters are considered in great detail in the completion design, the fracture conductivity receives lesser attention. On one side many feel that in extremely low permeability formations hydraulic fractures act as ‘infinitely conductive features’, even with minimal conductivity. On another side many factors that affect the effective conductivity acting in the hydraulic fracture are poorly understood or overlooked. This can lead to a disappointing outcome with wells producing below the reservoir potential. This paper presents a technique to assess the realistic fracture conductivity at downhole conditions, describe the relationship between conductivity and productivity and its economic implications in proppant selection. The effects of transverse fractures, low areal proppant concentration and flow dynamics, are also considered among other variables. Fracture modeling and actual field results will be presented to illustrate the optimization process. The case histories included in the paper show the successful implementation of this method in shale gas and liquids rich formations.