Larry Griffin

Breaking Up is Hard to Do: Creating Hydraulic Fracture Complexity in the Bakken Central Basin

The Bakken drilling boom in North Dakota has seen a frenzy of activity over the past several years as operators sought to hold acreage and create value with the drill bit. This has been particularly true in the Central Basin portion of the Williston Basin where initial wells drilled prior to 2008 were uneconomic. However, advances in completion technology caused such a fundamental shift in economics that the whole Central Basin area of over 2500 square miles has been opened to economic development with ~100 rigs currently drilling in the region. The most fundamental change in completion design has been the incorporation of “high-intensity” multi-stage fracturing. What makes Bakken completion design fundamentally different from recent shale gas developments has been the widespread use of uncemented liners with external packers in the open-hole lateral in order to create the multi-stage zonal isolation. As operators have advanced the application of multi-stage completion techniques there has been a wide variety of completion equipment used and stimulation designs that have been pumped. This operator decided to employ a completion design that comprised: (i) An open-hole “uncemented” liner section; (ii) Annular zonal isolation created by swell packers; (iii) The use of “plug and perf” technology to individually open successive zones to stimulation; (iv) The pumping of slickwater fracture treatment fluids at high rate; (v) The use of high-quality ceramic proppant to generate the required fracture conductivity. Production data are presented from 58 wells in which this completion and stimulation design has been conducted, which show that the use of this approach has resulted in well performance that is 25-45% superior to any other Bakken completion technique. Geology The Bakken Formation (highlighted in red in Figure 1) is located within the Williston Basin, which spans southern Saskatchewan and Manitoba in Canada as well as North Dakota and Montana in the United States. The basin was formed as a subtle downwarping between the Superior Craton to the northeast and the Wyoming Craton to the southwest. The Williston Basin is a gently dipping basin with very little structural deformation, with the exception of a small number of structural features including the Nesson Anticline and the Cedar Creek Anticline, as shown in Figure 1. Figure 1—Location of the Williston Basin.

Development of an Advanced Hydraulic Fracture Mapping System

The project to develop an advanced hydraulic fracture mapping system consisted of both hardware and analysis components in an effort to build, field, and analyze combined data from tiltmeter and microseismic arrays. The hardware sections of the project included: (1) the building of new tiltmeter housings with feedthroughs for use in conjunction with a microseismic array, (2) the development of a means to use separate telemetry systems for the tilt and microseismic arrays, and (3) the selection and fabrication of an accelerometer sensor system to improve signal-to-noise ratios. The analysis sections of the project included a joint inversion for analysis and interpretation of combined tiltmeter and microseismic data and improved methods for extracting slippage planes and other reservoir information from the microseisms. In addition, testing was performed at various steps in the process to assess the data quality and problems/issues that arose during various parts of the project. A prototype array was successfully tested and a full array is now being fabricated for industrial use.