Review of Current Fracture Stimulation Techniques for Best Economics in Multilayer, Lower-Permeability Reservoirs

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCurrently, thousands of wells are being drilled every year in low-to moderate-permeability sandstone and carbonate reservoirs that have many distinct zones or layers that can contribute to production if adequately stimulated. In lowerpermeability reservoirs, and especially for CBM completions, well economics will limit how much can be spent on the stimulation portion of a completion program. Operators may have to execute a "balancing act" with the need to maximize return on investment (ROI) while trying to complete as many contributing zones as possible. This usually drives a well operator toward methods that can minimize the number of separate well interventions while maximizing the number of zones that can be effectively stimulated.This paper provides a State of the Art review on both old and newer completion/stimulation techniques that can help an operator accomplish production goals. When the fracturing treatments are pumped down the casing, different methods applied can vary from simple, single-stage fracturing treatments using "limited entry" perforating to multi-stage fracture treatments with bridge plugs (BP) or ball/baffle stage isolation. Additionally, there are various other techniques incorporating conventional tubing strings with or without packers or BP's, and even various methods for coiled-tubing (CT)-deployed treatments.A "scorecard" approach presented here may offer operators an improved understanding of when a certain completion method is appropriate or flawed, based on the operators' current understanding of specific reservoir characteristics of their field or well. Too often, a multilayer completion technique has been applied to several wells and later found to be a poor choice. The wrong choice may have been made because of a limited understanding of the completion method, or even of the reservoir itself. Often, an operator understands the variances of the reservoir, but does not realize the limitations that these variances should bring to the process of choosing the optimal simulation/completion method. In some cases, the choice has simply been made to take the low-cost completion/stimulation approach, and the resulting well(s) did not produce at (or sustain) economic levels.

Axial Force Calculation Model for Completion String with Multiple Point Resistances in Horizontal Well

“…The advantages of horizontal wells are particularly obvious. More than 70% of the horizontal wells drilled in the mid-1990s were completed in such reservoirs [3][4][5]. The study of horizontal well reservoir fracturing stimulation technology began in the 1980s.…”

“…The ability to accurately calculate the axial force of the whole string from the bottom to the wellhead by calculating the deformation, contact force, and friction force; (2) The division of the resistance into pull-up resistance, run-down resistance, and bi-directional resistance can describe the tool effect more accurately; (3) In the calculation of the axial force, the numerical method is used to calculate the relationship between the contact force and the axial force; (4) The description of the force and deformation of the string with the packer in the curved wellbore with the third-order differential equation, allows for the resistance of the string near the centralizer and packer to be obtained by numerical simulation; (5) The ability to quickly judge the key position and key cause in case of jamming.…”

Evaluation of Multi-stage Fracturing by Hydrajet, Swellable Packer, and Compressive Packer Techniques in Horizontal Openhole Wells

“…As tight gas reservoirs tend to produce at low rates with lower ultimate recoveries, minimizing trips in an openhole well, placing more effective stimulation treatments, and optimizing rig and fracture equipment are the major factors to maximize profits. A single trip, multistage isolation, fracturing approach was developed (McDaniel, 2005, Pongratz et al, 2008, Stanojcic et al, 2010, Cramer, 2008.…”