Real-Data Fracture Analysis Enables Successful Hydraulic Fracturing in the Point of Rocks Formation, Kern County, California
Authors: Minner W.A. , Molesworth G.R. , Wright C.A. , Wood W.D. 
Published: December 2007

In 1994 and 1995, a series of hydraulic fracture stimulation treatments were performed in the Mc Kittrick field Point of Rocks formation, a thick &gt;2000') marine sequence of low permeability (0.1 ml)) sandstone intervals separated by shales. The thick interval, 10,000' depth, and a formation temperature of nearly 300 F posed challenges to effectively completing the desired intervals.

In general, the initial series of treatments targeted large gross perforation intervals and incorporated a large pad fraction. The treatments included few procedures to enable engineering evaluation of actual in-situ fracture behavior, which was later found to be very different from theoretical or pre-job estimates. Due to some combination of fracture treatment design and reservoir limitations, the production response results from the 1994-995 treatments were mixed, resulting in marginal overall project economics.

In 1996, six additional fracture treatments were performed in a new Point of Rocks well, No. 733-17Z. However, a very different fracture design methodology was utilized, focusing on real-data (net pressure) analysis. Objectives for these treatments included a) to place a more effective stimulation than resulting from past efforts, b) to characterize fracture behavior so that reasons for success or failure were clear, and c) to begin the process of optimizing treatment design. A more surgical fracturing strategy was employed, targeting selected Point of Rocks intervals using small perforation intervals and multiple independent fracture stages. Changes were also made to more effectively place fracture conductivity in the intended intervals, including a dramatic reduction in pad fraction and an increase in maximum proppant loading. These changes were implemented with the support of real-time fracture pressure analysis, enabling on-site diagnosis of proppant placement problems, and final treatment design refinement based on observed fracture behavior.

Compared with past treatment results, the new hydraulic fracture strategy resulted in a dramatically improved production response. With initial commingled production of over 6 mmscfd and 200 bopd (over 1200 boegd), well 733–17Z had a larger IP and has not experienced the rapid production decline of the previous Point of Rocks wells. With this success, the use of real-data fracture engineering will continue; there remains significant potential for treatment optimization in further planned field development.

Introduction

This paper presents a case history of the application of real-data (net pressure) fracture analysis, which was used to support the successful implementation of an aggressive fracture strategy in a reservoir with marginal past fracturing success. While this project did not utilize or develop a new or unique fracture design, it provides a solid example of the value of real-data fracture engineering.

The thesis of real-data analysis is that real-world hydraulic fracture behavior is extremely complex and affected by many unknown and variable factors. Thus, fracture modeling without utilization of real-data feedback (the norm until recently) may be at best useless, if not counter productive. As an analogy, what is the value of a reservoir performance prediction without the calibration provided by a production history or pressure buildup?

The feedback for real-data fracture analysis is in the form of net pressure behavior. Net pressure is the pressure in the main body of the fracture minus closure pressure. Net pressure is the single most important fracturing variable, because it is directly connected to the relationship between fracture length width, and height.

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