Shale Exploration Methodology and Workflow
- Jason L. Pitcher (Halliburton Energy Services Group) | Dan Buller (Halliburton Energy Services Group) | Mike Mellen
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Unconventional Gas Conference and Exhibition, 23-25 January, Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.8.4 Shale Oil, 5.6.2 Core Analysis, 4.3.4 Scale, 5.5.2 Core Analysis, 5.4.2 Gas Injection Methods, 1.11 Drilling Fluids and Materials, 5.8.2 Shale Gas, 1.2.2 Geomechanics, 1.6.9 Coring, Fishing, 6.5.4 Naturally Occurring Radioactive Materials, 5.2 Reservoir Fluid Dynamics, 2 Well Completion, 2.2.2 Perforating, 1.12.1 Measurement While Drilling, 7.2.3 Decision-making Processes, 1.6 Drilling Operations, 1.2.3 Rock properties, 4.2 Pipelines, Flowlines and Risers, 1.6.6 Directional Drilling, 5.1.5 Geologic Modeling, 5.6.1 Open hole/cased hole log analysis, 1.12.2 Logging While Drilling, 2.4.3 Sand/Solids Control, 4.6 Natural Gas, 5.1.1 Exploration, Development, Structural Geology
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Exploration for shales has become an integral part of many operators' processes in the North American shale boom. While leveraging public data in existing plays is a major advantage, when looking outside those existing areas, a comprehensive plan must be developed. The shale-exploration methodology is fundamentally different from conventional exploration, with different drivers and metrics.
Shale exploration requires an exploration program that includes a heavy data-acquisition element. Beyond the initial geological identification of the prospect, wells need to be drilled to evaluate the potential of the shale prospect. Extensive coring, open-hole logging and formation pressure testing are required to answer four basic questions: Does the shale have enough total organic content? Does the shale have the thermal maturity necessary? Does the shale have the stimulation potential? Does the sale have a simple structural environment conducive to horizontal drilling? Once these questions have a satisfactory answer, the key shale properties can be mapped using multiple sources with the goal of identifying core areas suitable for further horizontal well evaluation.
This paper describes the process and workflow for a data-acquisition program and demonstrates not only the benefits of acquiring specific data, but also highlights the uses of the data to aid the exploration decision process. Examples are given of the type data acquired, and the analytical workflow is discussed.
The first step in exploring for productive organic mudstone reservoirs is basin screening. This is done using regional geological studies along with any existing information available from the area under examination. Typically, shales that caused problems during drilling for conventional targets are seen as potential systems for further investigation. Once a basin has been identified using the screening tools outlined below, exploratory wells need to be drilled to acquire hard data.
In the hunt for potential shale reservoirs, it is common practice to fall back on conventional exploration techniques that have been used for many years. Tried-and-true methods of evaluating potential conventional reservoirs are looked at first, as this is within the comfort zone of many exploration departments. This approach has proven to be a difficult one, as shales exhibit distinctive properties that are not easily captured by conventional techniques. Metrics used for evaluating conventional reservoirs do not hold for the majority of unconventional shale plays. An example of this would be using resistivity measurements to determine water saturation. In most shales, water is clay bound and irreducible, so deriving water saturation is unnecessary.
Passey et al., in their 2010 paper, give a description of shale gas reservoirs and the scope of measurements made to determine the geological and petrophysical characterization or these systems. Information required to determine the potential viability of a particular play includes total organic carbon (TOC), maturity level (vitrinite reflectance), mineralogy, thickness, and organic matter type. Total gas, free gas, and adsorbed gas are important characteristics, as is porosity. Porosity in particular is a complex measurement in organic mudstone systems.
While the above measurements are key to the viability of a potential shale play, experience has shown that geomechanics and the ability to successfully stimulate using hydraulic stimulation methods is of equal importance. Any exploration program needs to measure the propensity of the rock to fracture with sufficient complexity to generate enough surface area for sustainable production rates.
Another consideration in rank exploration is the availability of tools and equipment to perform some of the specialized tests and data-acquisition programs. This is an important consideration when determining what is necessary and what is a luxury in terms of data acquisition (Kundert and Mullen 2009).
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