Hydraulic fracturing and horizontal drilling are the two key technologies that have made the development of unconventional shale formations economical. Hydraulic fracturing has been the major and relatively inexpensive stimulation method used for enhanced oil and gas recovery in the petroleum industry since 1949. The multi-stage and multicluster per stage fracture treatments in horizontal wellbores create a large stimulated reservoir volume (SRV) that increases both production and estimated ultimate recovery (EUR). This paper presents a new analytical solution methodology for predicting the behavior of multiple patterned transverse vertical hydraulic fractures intercepting horizontal wellbores. The numerical solution is applicable for finite-conductivity vertical fractures in rectangular shaped reservoirs. The mathematical formulation is based on the method of images with no flow boundaries for symmetrical patterns. An economics procedure is also presented for optimizing transverse fracture spacing and number of fracture stages/clusters to maximize the Net Present Value (NPV) and Discounted Return on Investment (DROI). The advantages of this approximate analytical production solution for multiple finite-conductivity vertical transverse fractures in horizontal wells and corresponding optimization procedure include: 1) the solution is based on fundamental engineering principles, 2) the production and interference of multiple transverse fractures are predicted to a first-order, and 3) it provides the basis for optimizing fracture and cluster spacing based on NPV and DROI, not just initial production rate. The methodology provides a simple way to predict the production behavior (including interaction) and associated economics of multi-stage/multi-cluster transverse fracture spacing scenarios in horizontal wellbores. The high initial production (IP) rates from multiple transverse fractures and the late time production decline as a result of fracture interference is discussed. Numerous examples are presented illustrating the method for optimizing (maximizing NPV and DROI) multiple transverse vertical hydraulic fractures in horizontal wellbores. Application of this technique will help provide the design engineer with a better tool for designing and optimizing multi-stage/multi-cluster transverse hydraulic fractures in horizontal wellbores. The governing production equations and fundamental procedure for NPV and DROI optimization of transverse fractures in a horizontal wellbore are discussed.
Multiple stage hydraulic fracturing is a key technology driving the development of unconventional resources in North America. This technique began in the Barnett shale and its application has opened the door for the successful development of nearly every shale play in the world, including the Eagle Ford shale. Given the relatively new application of this technique, and the number of fracture treatments completed, initial fracture treatment designs in a given play are often transferred from other North American shale plays to serve as baseline treatments. Given the rapid pace of development in a new play, as well as the desire to get to a standardized completion program, many operators continue to use these baseline designs and fail to evaluate current designs to develop more optimal treatments. This paper will discuss the successful evolution of hydraulic fracture designs in the Eagle Ford shale from one operator's perspective. It will detail the development from the traditional low conductivity slick water fracture treatments used initially in the play, to the use of higher conductivity hybrid fracture designs. In addition to detailing the theory and workflow of these design changes, this paper will also evaluate production data from multiple wells and evaluate production results for the hydraulic fracture designs. Discussion of enhanced conductivity will be presented along with the economic benefit of these changes. Those working the Eagle Ford shale can directly apply the principles presented in this paper to enhance the productivity and economics of their completions. In addition, engineers working other resource developments can use the principles from this paper to compare their current fracture design methodology and develop best practice approaches for hydraulic fracture design optimization in their respective plays.
This paper will evaluate the efficiencies of completion methods in a South Texas field utilizing the latest techniques in post fracture production analysis.Stimulation effectiveness for each frac stage in ten multi-zone wells is evaluated. Effective values for reservoir and fracture parameters including porosity, permeability, propped fracture half-length, fracture conductivity and fracture face skin will be derived using production analysis techniques and will be compared for the different completion methods employed.The holistic model will incorporate the geological, petro-physical properties of the formation and production logging data. Actual stimulation and production data from ten wells in the same area are used in this analysis. Five of the wells were completed in single-stage fracture stimulation across multiple perforated intervals.Five wells were completed with two-stage fracture stimulations across multiple perforated intervals.The multiple layer fracturing technique was utilized in all wells. The study will derive the effective reservoir and fracture parameters using production allocation for each interval in the multiple interval wells. This paper will compare the different completion techniques using this methodology and will discuss a predictive model for future stimulation work in this area.This methodology will also help in identifying under-stimulated zones in existing wells that may be candidates for re-fracturing. Introduction The wells included in the study are part of the Wilcox Lobo Trend located in Zapata County in South Texas.The Wilcox (Lobo) trend in Webb and Zapata counties is a series of geopressured, low permeability sands with an average depth from 5,000 to 12,000 ft (1,525 to 3,660 m).The Lobo section consists of a sequence of stacked Paleocene age sands and shales overlain by the Lower Wilcox shale of Eocene Age.Extensive faulting, present in the Lobo section, has resulted in a slump complex of rotated fault blocks.The Lobo trend extends from Webb and Zapata counties to the south and west into Mexico (Figure 1).Effective permeabilities are less than 0.1 md.Implementing an effective hydraulic fracture treatment and an evaluation process for stimulation effectiveness are requirements to economically produce the low permeability sands in the Lobo trend. The wells presented here are nearby offset wells in the Lobo field (Figure 2). These wells were completed in 2003.The target intervals in these wells are primarily three zones.All the wells were fractured with similar fracturing fluids, intermediate strength proppants and aggressive breaker schedules utilizing multiple layer fracturing techniques. Background Extensive work has been conducted around fracture treatment design and evaluation of wells with multiple zones with most of the work focused on the use of limited entry techniques to effectively place proppant across multiple zones [1,2,3,4].The limited entry technique utilizes perforation friction to divert designed fluid and proppant volumes into multiple zones.This method is utilized when the economics do not justify multiple stages or when multiple stages cannot be placed effectively[5].This technique has been successfully implemented in the Lobo field in numerous wells.The success comes from applying the formation evaluation and log analysis into a fracture modeling process, and from the use of limited entry design guidelines [6,7].Tracer surveys and production logs were obtained after numerous stimulation treatments to develop these guidelines.However, tracer surveys provide an estimate of the fracture height and production logs provide contributions from each zone in a snapshot of time.
Multi-stage/multi-cluster hydraulic fracturing in horizontal wellbores is a key technology driving the development of unconventional resources in North America. Several engineering technologies developed over the past decade are readily available for operators to help enhance production. The advantages of technology integration for creating multiple transverse fractures in horizontal wellbores have been well documented.Given the rapid pace of development, many operators strive to standardize completion programs to drive consistency and efficiency in operations and well performance. The key parameters that maximize production in unconventional reservoirs are not dissimilar to the key parameters proven successful time and again in conventional completion designs and fracturing treatments. Generating fracture complexity may be important in unconventional reservoirs, but maximum reservoir contact does not necessarily translate to an effectively stimulated reservoir. Fracture length, fracture conductivity and fracture spacing in multi-cluster/multi-stage completions are first-order parameters that can be engineered. However, additional completion and design considerations for unconventional wells such as natural fracture saturation, mid-field fracture complexity, mechanical fracture interaction and transverse fracture production interference must be considered to enhance production and maximize economics. This paper will focus on technology integration for the Wolfcamp A reservoir using a discrete fracture network (DFN) model for predicting fracture geometry, formation evaluation, oil and fluid tracers, microseismic monitoring and production history matching. The methodology includes: 1) utilization of current fundamental engineering principles and procedures for completion design, 2) simulator calibration to improve predictive models and 3) production history matching and forecasting.Application of this integrated technology approach will help provide the operator with a systematic approach for designing, analyzing, and optimizing multi-stage/multi-cluster transverse hydraulic fractures in horizontal wellbores. Readers of this paper will gain insight on how sound engineering, fracture modeling and data integration can increase recovery and optimize completions in the Wolfcamp formations. Those working in the Delaware and Midland basins can directly apply the principles presented in this paper to enhance the productivity and economics of their completions.
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