N.R. Warpinski

Mapping Hydraulic Fracture Growth and Geometry Using Microseismic Events Detected by a Wireline Retrievable Accelerometer Array

Technology has advanced to the point where microseismic monitoring of hydraulic fractures can provide critical information for fracture optimization. Important elements of a monitoring system include the receivers, the telemetry system, and automatic processing of the vast amounts of data. Procedures and additional data requirements are discussed and examples of the important results which can be obtained are illustrated. Hydraulic fracturing is a critical technology for the exploitation of natural gas and oil resources, but its optimization has been impeded by an inability to observe how the fracture propagates and what its overall dimensions are. Recent field experiments in which fractures have been exposed through coring or mineback have demonstrated that hydraulic fractures are not the ideal, symmetric, planar features that are currently envisioned. Instead, they appear to commonly have multiple strands, secondary fractures, height and length asymmetries, and other complexities which make a priori predictions difficult. It is clear that model validation, fluid selection, proppant loadings, problem identification and solution, field development, and many other aspects of fracture optimization have been encumbered by the absence of ground-truth information on fracture behavior in normal field settings. Technology is now becoming available, however, to provide extensive diagnostic information on fracture growth, final size and geometry. Multi-level wireline receiver arrays for downhole passive imaging of fracture behavior have become viable and are demonstrating that hydraulic fractures can be imaged, assessed, and eventually controlled. These receiver arrays require high-quality transducers, well-designed clamping systems, high-speed telemetry, real-time processing capabilities, and careful procedures to be effectively used. This paper discusses this technology, its application and validation, and examples of the value of fracture imaging. It concentrates on a 5-level, accelerometer-based, fiber-optictelemetry system currently being used for microseismic mapping.

Microseismic and deformation imaging of hydraulic fracture growth and geometry in the C sand interval, GRI/DOE M-Site project

Six hydraulic-fracture injections into a fluvial sandstone at a depth of 4300 ft were monitored with multi-level tri-axial seismic receivers in two wells and an inclinometer array in one well, resulting in maps of the growth and final geometry of each fracture injection. These diagnostic images show the progression of height and length growth with fluid volume, rate and viscosity. Complexities associated with shut downs and high treatment pressures can be observed. Validation of the seismic geometry was made with the inclinometers and diagnostic procedures in an intersecting well. Fracture information related to deformation, such as fracture closure pressure, residual widths, and final prop distribution, were obtained from the inclinometer data.

The Mounds Drill-Cuttings Injection Field Experiment: Final Results and Conclusions

This paper summarizes the results obtained from a comprehensive, joint-industry field experiment designed to improve the understanding of the mechanics and modeling of the processes involved in the downhole injection of drill cuttings. The project was executed in three phases: drilling of an injection well and two observation wells (Phase 1); conducting more than 20 intermittent cuttings-slurry injections into each of two disposal formations while imaging the created fractures with surface and downhole tiltmeters and downhole accelerometers (Phase 2); and verifying the imaged fracture geometry with comprehensive deviated-well (4) coring and logging programs through the hydraulically fractured intervals (Phase 3). Drill cuttings disposal by downhole injection is an economic and environmentally friendly solution for oil and gas operations under zero-discharge requirements. Disposal injections have been applied in several areas around the world and at significant depths where they will not interfere with surface and subsurface potable water sources. The critical issue associated with this technology is the assurance that the cuttings are permanently and safely isolated in a cost-effective manner. The paper presents results that show that intermittent injections (allowing the fracture to close between injections) create multiple fractures within a disposal domain of limited extent. The paper also includes the conclusions of the project and an operational approach to promote the creation of a cuttings disposal domain. The approach introduces fundamental changes in the design of disposal injections, which until recently was based upon the design assumption that a large, single storage fracture was created by cuttings injections.

Evaluation of a downhole tiltmeter array for monitoring hydraulic fractures

A series of hydraulic-fracture experiments using a downhole tiltmeter array, called an inclinometer array, was conducted at the Department of Energy (DOE)/Gas Research Institute (GRI) Multi-Site facility in Colorado. The inclinometer array was used to measure the deformation of the reservoir rock in response to hydraulic fracture opening and confirm microseismically measured results. In addition, the inclinometer array was found to be a useful tool for accurately measuring closure stress, measuring residual widths of both propped and unpropped fractures, estimating proppant distribution, and evaluating values of in situ moduli.

The use of broadband microseisms for hydraulic-fracture mapping

The authors conducted a series of hydraulic-fracture experiments to examine improvements in seismic-fracture diagnostic technology that are available with the application of advanced receiver capabilities. They present characteristics of the microseisms, tool response behavior, and the results of the tests.

Improved Microseismic Fracture Mapping Using Perforation Timing Measurements for Velocity Calibration

Microseismic mapping of hydraulic fractures is improved by use of crosswell data to calibrate or verify dipole-sonic velocity data. The microseismic technique uses an array of triaxial receivers to detect microearthquakes induced by a fracture treatment to provide a real-time image of the fracture and the direction in which it propagates. To apply this technique, receiver orientation must be determined by detecting perforations or other energy sources in the treatment well. The ultimate goal is improved accuracy in microseismic mapping, but the results are useful in assessing the applicability of dipole-sonic logs.

Observations of Broad-Band Micro-Seisms During Reservoir Stimulation

During hydrocarbon reservoir stimulation such as hydraulic fracturing, the cracking and slippage of the formation results in the emission of seismic energy. The objective of this study was to determine the properties of these induced micro-seisms. A hydraulic fracture experiment was performed in the Piceance Basin of Western Colorado to induce and record micro-seismic events. The formation was subjected to four processes; breakdown/ballout, step-rate test, KCL mini-fracture, and linear-gel mini-fracture. Micro-seisms were acquired with an advanced three-component wall-locked seismic accelerometer package, placed in an observation well 211 ft offset from the well. During the two hours of formation treatment, more than 1200 micro-seisms with signal-to-noise ratios in excess of 20 dB were observed. The observed micro-seisms had a nominally flat frequency from 100 Hz to 1500 Hz and lack the spurious tool-resonance effects evident in previous attempts to measure micro-seisms. Both p-wave and s-wave arrivals are clearly evident in the data set, and hodogram analysis yielded coherent estimates of the event locations. This paper describes the characteristics of the observed micro-seismic events (event occurrence, signal-to-noise ratios, and bandwidth) and illustrates that the new acquisition approach results in enhanced detectability and event location resolution.

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.

Application of microseismic technology to hydraulic fracture diagnostics: GRI/DOE Field Fracturing Multi-Sites Project

The objective of the Field Fracturing Multi-Sites Project (M-Site) is to conduct field experiments and analyze data that will result in definitive determinations of hydraulic fracture dimensions using remote well and treatment well diagnostic techniques. In addition, experiments will be conducted to provide data that will resolve significant unknowns with regard to hydraulic fracture modeling, fracture fluid rheology and fracture treatment design. These experiments will be supported by a well-characterized subsurface environment as well as surface facilities and equipment conducive to acquiring high-quality data. It is anticipated that the project`s research advancements will provide a foundation for a fracture diagnostic service industry and hydraulic fracture optimization based on measured fracture response. The M-Site Project is jointly sponsored by the Gas Research Institute (GRI) and the US Department of Energy (DOE). The site developed for M-Site hydraulic fracture experimentation is the former DOE Multiwell Experiment (MWX) site located near Rifle, Colorado. The MWX project drilled three closely-spaced wells (MWX-1, MWX-2 and MWX-3) which were the basis for extensive reservoir analyses and tight gas sand characterizations in the blanket and lenticular sandstone bodies of the Mesaverde Group. The research results and background knowledge gained from the MWX project are directly applicable to research in the current M-Site Project.