Drilling Optimization in Unconventional and Tight Gas Fields: An Innovative Approach
- Keith Richard Holdaway (SAS Institute Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Unconventional Gas Conference and Exhibition, 31 January-2 February, Muscat, Oman
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 3 Production and Well Operations, 5.8.1 Tight Gas, 5.6.11 Reservoir monitoring with permanent sensors, 2 Well completion, 4.6 Natural Gas, 1.6.3 Drilling Optimisation, 2.4.3 Sand/Solids Control, 3.2.4 Acidising, 7.6.4 Data Mining, 6.1.5 Human Resources, Competence and Training, 3.3.1 Production Logging, 1.12.2 Logging While Drilling, 2.7.1 Completion Fluids, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.1.2 Faults and Fracture Characterisation, 1.14 Casing and Cementing, 1.6.1 Drilling Operation Management, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 5.1 Reservoir Characterisation, 4.3.4 Scale, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6 Drilling Operations, 1.8 Formation Damage, 1.2.2 Drilling Optimisation, 1.2.2 Geomechanics, 7.6.6 Artificial Intelligence, 5.6.9 Production Forecasting
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The majority of the technically recoverable natural gas is present in unconventional reservoirs such as tight sands, shale, and coal beds. On account of the implicit high costs associated with these unconventional and deep gas assets, it is of paramount importance to garner as much knowledge from potentially disparate and limited data sources. The objectives must be minimization of drilling and completion times, constraint of risks, quantification of uncertainty and ultimately maximization of the lifetime of a well's productivity.
This paper illustrates an advanced analytical methodology that aggregates and integrates data from a multitude of sources, performs a robust quality control, correlates and discovers patterns to enable engineers to determine more efficient and accurate exploitation strategies. It proposes an approach based on an advanced analytical framework that introduces an exploratory data analysis step for reservoir characterization, followed by determination of key production indicators and multivariate methodologies to classify wells. With improved understanding of inherent correlation between geology, reservoir, rock mechanics, frackpack process and proppant fluid and well performance, it is feasible to cluster the wells in accordance to the overriding production indicators, thus dividing the field into clearly defined segments. The statistical output enables mapping via a transparent classification of best possible wells to known geology and reservoir conditions to identify and locate poorly-drained zones and effectively neccessitate less drilling to achieve production targets.
Well stimulation is a well intervention performed on an oil or gas well to increase production by improving the flow of hydrocarbons from the drainage area into the well bore. Stimulation is performed on a well to increase or restore production. Sometimes, a well initially exhibits low permeability, and stimulation is employed to commence production from the reservoir. Other times, stimulation is used to further encourage permeability and flow from an already existing well that has become under-productive.
One type of stimulation treatment, acidizing is performed below the reservoir fracture pressure in an effort to restore the natural permeability of the reservoir rock. Well acidizing is achieved by pumping acid into the well to dissolve limestone, dolomite and calcite cement between the sediment grains of the reservoir rocks. There are two types of acid treatment: matrix acidizing and fracture acidizing: a matrix acid job is performed when acid is pumped into the well and into the pores of the reservoir rocks. In this form of acidization, the acids dissolve the sediments and mud solids that are inhibiting the permeability of the rock, enlarging the natural pores of the reservoir and stimulating flow of hydrocarbons. While matrix acidizing is done at a low enough pressure to keep from fracturing the reservoir rock, fracture acidizing involves pumping highly pressurized acid into the well, physically fracturing the reservoir rock and dissolving the permeability inhibitive sediments. This type of acid job forms channels through which the hydrocarbons can flow. Acid is then forced into the newly formed fractures to dissolve more rock and open up a deep channel for petroleum flow. The acid is held under pressure for a short period of time to allow it to react with the formation matrix. The spent acid is then flowed or swabbed out of the well, after which the well is put back into production. Acidizing is most often used for two functions: increasing permeability throughout the formation and cleaning up formation damage near the wellbore caused by drilling or completion fluids.
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