James L. Hunt

Fracturing aspects of horizontal wells

This paper discusses the main reservoir engineering and fracture mechanics aspects of fracturing horizontal wells. The paper discusses fracture orientation with respect to a horizontal wellbore, locating a horizontal well to optimize fracture height, determining the optimum number of fractures intercepting a horizontal well, and the mechanism of fluid flow into a fractured horizontal well.

Evaluation and completion procedure for produced brine and waste water disposal wells

Abstract Waste water disposal is one of the many environmental issues becoming increasingly difficult to deal with. A single disposal well may not be sufficient to handle the large volume of waste water generated by many industrial plants. Increasing the injectivity of a well by hydraulic fracturing is a viable solution to this problem. This paper discusses the application of a numerical water injection simulator to evaluate a low-permeability sandstone reservoir for waste water disposal. The injection model is used to study the effects and feasibility of hydraulically fracturing the reservoir to improve injectivity. Also discussed are the field implementation of the hydraulic fracturing treatment, testing of the well to evaluate the treatment, and a comparison of observed and simulated injectivity.

Production-systems analysis for fractured wells

Production-systems analysis has been in use for many years to design completion configurations on the basis of an expected reservoir capacity. The most common equations used for the reservoir calculations are for steady-state radial flow. Most hydraulically fractured wells require the use of an unsteady-state production simulator to predict the higher flow rates associated with the stimulated well. These high flow rates may present problems with excessive pressure drops through production tubing designed for radial-flow production. Therefore, the unsteady-state nature of fractured-well production precludes the use of steady-state radial-flow inflow performance relationships (IPRs) to calculate reservoir performance. An accurate prediction of fractured-well production must be made to design the most economically efficient production configuration. It has been suggested in the literature that a normalized reference curve can be used to generate the IPRs necessary for production-systems analysis. However, this work shows that the reference curve for fractured-well response becomes time-dependent when reservoir boundaries are considered. A general approach for constructing IPR curves is presented, and the use of an unsteady-state fractured-well-production simulator coupled with the production-systems-analysis approach is described. A field case demonstrates the application of this method to fractured wells.

Design and Analysis of Fractured Horizontal Wells in Gas Reservoirs

Although horizontal wells may offer significant production improvement over vertical wells, it may be necessary to fracture horizontal wells to maximize their return on investment. This is especially true in the case of tight gas formations. This paper presents a model for fractured horizontal wells operating under constant pressure conditions, which is most suitable for producing tight gas reservoirs. The created fracture may be longitudinal or transverse. In this paper we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented. The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points-of-view is presented. Also included is a short discussion of field examples. Because performance of a longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outerfractures outperform the inner fractures. However, more than two fractures are necessary to efficiently produce the reservoir for most cases. A simplified economical analysis supports this conclusion.

Well-Test Analysis Following a Closed-Fracture Acidizing Treatment

A new model representing fluid flow in a reservoir treated with closed-fracture acidizing (CFA) is presented. The model is characterized by a low-conductivity fracture (representing the closed fracture) and highly conductive wormholes (owing to acid flow). Application of the model to pressure-transient data analysis following a CFA treatment is presented through a field example.

Reservoir Engineering Aspects of Fracturing High Permeability Formations

High permeability formations are not usually the realm of hydraulic fracturing. However, recently there has been a resurgence of interest in stimulating these reservoirs. Reasons for the interest include fracturing past damaged zones, controlling and preventing sand production, and generally providing better control over the wellbore. In studying this problem, several factors need to be considered. One factor is the productivity improvement aspect of the fracturing treatment. Under certain conditions, fracturing can provide a significant production increase even in a very highly permeable formation. Therefore, production versus time is important. A second consideration is pressure as a function of distance. This factor is important in the sand production aspect. Fracturing can decrease the pressure drop and gradient within the formation and thus sand production can be controlled or even prevented. This paper presents results of a study performed to investigate the effect of various parameters on well and fracture performance in a high permeability reservoir. These parameters include formation permeability, degree and depth of damage, fracture length, fracture conductivity, and fracture face damage. Conclusions from the study provide guidelines for candidate selection and fracture design as well as insight into the effect of stimulation of high permeability reservoirs.