The Practical Application of Economic Well Performance Criteria to the Optimization of Fracturing Treatment Design
Authors: Anderson R.W. , Phillips A.M. 
Published: December 2007

SPE Members

Low permeability reservoirs are currently being propped with sand, resin coated sand, intermediate density proppants and bauxite. This wide range of proppant cost and performance has resulted in the proliferation of proppant selection models. Initially, a rather vague relationship between well depth and proppant strength dictated the choice of proppant. More recently, computerized models of varying complexity have become available which utilize net present value calculations. The input is based on the operator's performance goals for each well and specific reservoir properties. Simpler, non-computerized approaches also being used include cost/performance comparisons and nomographs. Each type of model, including several of the computerized models, will be examined.

Utilizing these models and net present value calculations, optimum fracturing treatment designs have been developed for low permeability reservoirs such as the Prue in Oklahoma. Typical well conditions are used in each of the selection models and the results are compared. The computerized models allow the operator to determine, prior to fracturing, how changes in proppant type, size, and quantity will affect post-frac production over time periods ranging from several months to many years. Thus, the operator can choose the fracturing treatment design which best satisfies his economic performance goals for a particular well, whether those goals be long term or short term oriented.

INTRODUCTION:

In the design of a hydraulic fracturing treatment, one of the primary considerations is the fracturing fluid - its temperature stability, proppant transport capability, and possible interactions with the formation. However, the only part of the fracture treatment which remains and controls long term productivity from a well is the proppant which is placed in the fracture. As a result, placement of the correct type, size, and amount of proppant for the given reservoir and producing conditions is of primary importance.

Before the correct proppant can be selected, it is first necessary to optimize the propped fracture length based on the reservoir conditions. Theoretically, fracture flow capacity is optimized such that a dimensionless conductivity of at least 10 is obtained. The theory and application of dimensionless conductivity has been well documented in the literature.

In reality, fracture length is influenced to a great extent by operator budgets, common area practices and fluid properties. Based on these considerations and reservoir properties, penetration distance and proppant concentration profile are obtained using fracture design programs. A dimensionless conductivity of 10 cannot always be economically or operationally obtained. To complicate matters, there are now a variety of proppant types and sizes available, some of which vary greatly in cost, and most of which have overlapping application ranges.

The purpose of the computerized proppant selection model is to determine how post-frac productivity will be affected by changes in proppant type, size, and quantity. Net present worth calculations are then applied so that the technical choices are expressed in economic terms. This allows the operator to choose the fracturing design which best fits his economic performance goals for the well.

DESCRIPTION OF REPRESENTATIVE MODELS

The simplest methods of proppant selection are in the form of graphs and nomographs.

P. 83^