The Dimensionless Productivity Index as a General Approach to Well Evaluation
- Iskander R. Diyashev (Sibneft Oil) | Michael J. Economides (U. of Houston)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- August 2006
- Document Type
- Journal Paper
- 394 - 401
- 2006. Society of Petroleum Engineers
- 1.6 Drilling Operations, 2.4.3 Sand/Solids Control, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.2.2 Perforating, 5.7.3 Deterministic Methods, 1.6.6 Directional Drilling, 2 Well Completion, 1.8 Formation Damage, 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.6.3 Deterministic Methods, 4.1.2 Separation and Treating, 5.6.9 Production Forecasting, 2.5.1 Fracture design and containment
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Petroleum-well performance and its evaluation are clearly some of the most important functions of modern production engineering. We present a general approach to the issue by employing the field-derived, dimensionless productivity index (JD ), which we calculate from measured information including the production rate, reservoir and flowing pressures, and well and reservoir data.
The JD is independent of well completion (i.e., it transcends the geometry), whether the well is under radial flow, is hydraulically fractured, or whether it is vertical or horizontal. The determined JD s are then compared against benchmarks we have developed for optimized production, such as the concept of unified-fracture design (UFD) or maximized horizontal well performance. We have developed deterministic methods for this analysis and new means to depict the results graphically.
Such evaluations are important in concluding whether the well is underperforming or whether past engineering could have been improved and by how much. Decisions such as refracturing, the redesign and improvement of future treatments, and whether to fracture vertical or drill horizontal wells can be readily made.
The production (or injection) of an oil or gas well is of fundamental concern in petroleum engineering. There are many well-known approaches to tracking the problem, some use analytical mathematical approximations, while others are more involved and use numerical simulation schemes. For single-well performance, the analytical approximations are often quite adequate, and we will use them in this work.
Traditionally, the well inflow is derived from Darcy's law in radial coordinates with added boundaries: the near-well condition is characterized by a skin effect, while the outer boundaries can be distinguished as constant pressure (steady state) or no-flow (pseudosteady state.) For radial-flow geometry, the expressions are quite rudimentary. Irregular drainage shapes and asymmetrical well positions can be accounted for by use of shape factors. On occasion, transient conditions are assumed with infinite-acting boundaries, but such situations are generally of no practical use for the production prediction and evaluation of almost all but the lowest-permeability reservoirs.
The pseudosteady-state condition is the one that is the most interesting for the forecast of future well performance because it accounts for reservoir-pressure depletion. The latter requires material-balance calculations that relate this depletion to the underground fluid withdrawal.
|File Size||1 MB||Number of Pages||8|
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