Dynamic Production System Nodal Analysis

Abstract

SPE Member Abstract A Dynamic Production System Nodal Analysis (DPSNA) Technique has been developed, verified, and applied to wells in the Kuparuk River Field. This analytical technique combines reservoir performance models, nodal analysis for individual wells, and calculation of pressure drop in the network of surface lines to obtain a global analysis of the production system through time. Evaluation of the DPSNA Technique was performed using well test data from twenty-five wells in the Kuparuk River Field. Each well in the analysis contained two productive intervals. The DPSNA Technique was able to predict the effect of a producing zone control strategy on oil, gas, and water production from these wells. Introduction The objective of DPSNA is to determine the incremental rate impact of a production system project or projects. Applications of this analytical technique include evaluation of: surface line looping: production zone control strategies, well stimulation, and gas lift. In essence, the DPSNA Technique is a nodal analysis of all the producing wells in the system through time. The typical nodal analysis (1, 2, 3) is performed on a single well for a given point in time. Nodal analysis involves the simultaneous solution of inflow performance and tubing and surface line pressure loss correlations to obtain pressures and flow rates through the system. In this analysis the entire production system is analyzed simultaneously. This allows the analysis to include the impact of a given well's production on the other wells in the system. Because DPSNA has a time dimension, changes in reservoir pressure, water saturation and gas oil ratio through time need to be considered. This is accomplished by interfacing the inflow performance computation in the nodal analysis with a reservoir performance model. In this analysis the reservoir performance model is simply the summation of the results of a reservoir simulation run. Since the projects being evaluated will have the effect of accelerating production, the reservoir simulation results are summarized with respect to cumulative production rather than time. For each time step the DPSNA Simulator converges on now rates that satisfy reservoir and inflow performance models and surface line and tubing hydraulics correlations. Flow rates and pressures for the entire production system are reported through time. Mechanisms are provided to simulate infill drilling, production zone control strategies, well stimulation, and gas lift. Figure 1 illustrates a typical incremental rate stream for a rate acceleration project such as a surface line loop. Using the DPSNA Simulator this information can be generated with two simulations, one run which does not incorporate the effects of the project under evaluation, and another run which models the project under consideration. This incremental rate stream can then be used in an economic evaluation to determine the present value of the project. The reservoir performance model allows for the inclusion of results of reservoir simulation in the production system analysis. This is achieved wit out the disadvantages of excessive computation time and convergence problems associated with the combination of reservoir and production system simulation in a single simulator program (4, 5). Reservoir Simulation The Kuparuk River field on the Alaskan North Slope produces from two stratigraphically independent sands of the Kuparuk River Formation. A full field reservoir model was constructed to support field management and development planning (6). The Kuparuk Full Field Reservoir Model (KFFM) was assigned overall area) dimensions of 19 and 22 miles in the x and y directions, respectively, to encompass the entire field. The model contains 20,064 gridblocks (40 acres each) in a uniform grid distributed over three layers. Two layers for the relatively high permeability upper sand (C Sand) and one layer for the lower producing sand (A Sand). The grid was oriented with the major north/south fault trend to capture the directional influence of structural and stratigraphic aspects on fluid movement. Currently the simulator models a total of 719 wells. P. 265^