Managing Sand Production - The Key to Improved Well Deliverability and Extended Field Life
- Christian K. Enzendorfer (OMV UK Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2007
- Document Type
- Journal Paper
- 165 - 173
- 2007. Society of Petroleum Engineers
- 1.6 Drilling Operations, 2.5.2 Fracturing Materials (Fluids, Proppant), 3 Production and Well Operations, 5.6.4 Drillstem/Well Testing, 3.2.5 Produced Sand / Solids Management and Control, 3.2.4 Acidising, 2.2.2 Perforating, 5.6.8 Well Performance Monitoring, Inflow Performance, 5.5.2 Core Analysis, 1.2.3 Rock properties, 4.1.2 Separation and Treating, 5.1.1 Exploration, Development, Structural Geology, 2.4.3 Sand/Solids Control, 5.2 Reservoir Fluid Dynamics, 4.1.5 Processing Equipment, 2.4.5 Gravel pack design & evaluation, 2.4.6 Frac and Pack, 4.2 Pipelines, Flowlines and Risers, 1.8 Formation Damage
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This paper deals with a case study of a high-rate sour-gas field in Pakistan. The paradigm shift from sand control to sand management boosted production rates by more than 100%. At the same time, higher wellhead pressures and less drawdown will extend field life and ultimate recovery. Major investments such as wellhead or field front-end compression could be delayed and, thereby, appreciable cost savings could be generated.
After initial well test results, it was concluded that all wells in the Miano gas field will need gravel-pack installations to protect completion and surface equipment. Only after 2 years of production at high rates in excess of 50 MMscf/D was it found that the installed gravel packs reduce flow rates severely. The paper will demonstrate how, through reinterpretation of data that formed the basis for the previous decision to gravel pack the wells and a thorough evaluation of sand-production potential and risks, a successful sand-management strategy was deployed. Existing gravel packs were perforated, and later production wells have been completed without gravel packs beforehand. Rigorous monitoring of surface equipment by means of erosion probes, ultrasonic wall-thickness measurements, and choke-performance charts has been introduced to ensure safe production operations.
From drillstem tests (DSTs) on exploratory and appraisal wells in the Miano gas field, it was predicted that sand production would occur during field production. In consequence, a sand-control strategy was formulated on the basis of complete sand exclusion, because zero sand-production tolerance was believed to be mandatory in high-rate gas wells. To achieve this goal, all wells were completed with gravel packs inside the 7-in. liners. These internal gravel packs (GPs) consisted of two joints of 4½-in. wire-wrapped screens, of either 12- or 20-gauge slot width based on grain-size analysis from produced-sand samples, packed with 20/40 US mesh and 12/20 US mesh gravel sand, respectively. A strong focus was maintained on applying best practices during perforation and gravel-pack operations. These included underbalanced perforations [800 to 1,000 psi underbalance, 4½-in. tubing-conveyed perforation guns, 12 shots per foot (spf)], cleanout flow before gravel-pack operations, pickling of the gravel-pack string, pregravel-pack acidizing of the perforations, filtering of all fluids down to 4-µ particle size, and ensuring proper packing by use of squeeze and circulating modes. A maximum value for differential pressure resulting from damage and turbulence skin across the gravel-pack completion was set at 500 psi for the anticipated maximum rate of 50 MMscf/D, on the basis of findings from literature research. Initial production rates were as expected, but soon after start of production, the first well-performance problems occurred. The flowing wellhead pressures (FWHPs) declined faster than expected from material-balance calculations. It was quite evident, and confirmed by pressure-buildup analysis, that skin was increasing in the downhole completion. This was attributed to reservoir fines being mobilized and produced into the gravel pack and thereby plugging it. The safe limit of 500-psi maximum drawdown was soon exceeded in an effort to maintain production at the committed level.
Acid-stimulation treatments of gravel packs worked well to reduce the skin, but the effects were not long-lasting. Finally the original sand-control strategy of complete sand exclusion was abandoned and a sand-management strategy formulated. In principle, this allows the production of certain quantities of sand within the limits of safe production operations.
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