Harald Asheim

Models for petroleum field exploitation

Abstract This paper presents some models for an early evaluation of a petroleum field. Based on crude assumptions about a reservoir, our models suggest decisions concerning platform capacity, drilling programme and production. We start out with a simple production planning model using linear programming. By mixed integer programming techniques the model is gradually extended. The most sophisticated version of the model can propose platform capacity, where and when wells should be drilled, and the production from the wells. The models are tested on numerical examples, and the results are discussed. From the experiments we conclude that the problems are very hard to solve, and that the size of problems that can be solved is limited by the computational burden. Finally we give some ideas for future work that may provide better solution methods.

A flow resistance correlation for completed wellbore

Abstract The flow along horizontal wells differs considerably from conventional flow in pipes, because there is radial fluid inflow through the perforation. This inflow disturbs the flow velocity profile in the pipe which affects the pressure gradient along the wellbore. In this work a flow resistance model for horizontal well flow has been developed, allowing prediction of the effective friction factor due to both wall friction and fluid inflow. For a typical well, this revised friction factor may improve the accuracy of flow performance prediction by 10–30%. Experiments showed excellent agreement between these predictions and measurements.

MONA, an accurate two-phase well flow model based on phase slippage

In two-phase flow, both holdup and pressure loss are related to interfacial slippage. A computation model based on phase slippage has been developed that allows a priori estimation of the slip parameter values. By parameter optimization, the accuracy of the model can be improved. The model was tested with production-well data from the Forties and the Ekofisk fields and flowline data from Prudhoe Bay. It was considerably more accurate than the standard models that were used for comparison.

Holdup Propagation Predicted by Steady-state Drift Flux Models

Abstract For actual two phase pipe systems, variations in input flows often occur naturally, or may be imposed intentionally. Changes in holdup (in-situ fluid fraction) caused by such input variation will propagate along the pipe, and may affect overall performance. The current paper describes experimental investigation of holdup propagation in oil–water flow in a vertical pipe. It is shown that larger changes in input holdup profile may either compress or rarefy as they propagate along the pipe. For the cases considered, observed behaviour could be quite accurately predicted using a non-linear, hyperbolic wave propagation relation and a drift flux model, calibrated at steady-state flow conditions. The methodology outlined enables prediction and optimization of processes where the fluid content in a pipeline, or wellbore, is displaced by another, immiscible fluid.

Determination of perforation schemes to control production and injection profiles along horizontal wells

The flowing pressure drop along the wellbore gives rise to increasing drawdown in the direction of flow. Particularly for long horizontal wells, this may lead to strongly nonuniform inflow. Lithology variation has similar effects. For production wells, nonuniform inflow may aggravate cresting and cause premature breakthrough of gas or water. For water flooding, sweep efficiency often depends on uniform injection over long horizontal distances. Thus, control of the injection profile may be imperative to efficient recovery. The paper describes a scheme for control of production and injection profiles by means of perforation-density variation. The method developed enables determination of such perforation schemes on the basis of classical inflow efficiency concepts and models.

Bull heading to kill live gas wells

To kill a live closed-in gas well by bull heading down the tubing, the selected pump rate should be high enough to ensure efficient displacement of the gas into the formation (i.e., to avoid the kill fluid bypassing the gas). On the other hand, the pressures that develop during bull heading at high rate must not exceed wellhead pressure rating, tubing or casing burst pressures or the formation breakdown gradient, since this will lead, at best, to a very inefficient kill job. Given these constraints, the optimum kill rate, requited hydraulic horsepower, density and type of kill fluids have to be selected. For this purpose a numerical simulator has been developed, which predicts the sequence of events during bull heading. Pressures and flow rates in the well during the kill job are calculated, taking to account slip between the gas and kill fluid, hydrostatic and friction pressure drop, wellbore gas compression and leak-off to the formation. Comparison with the results of a dedicated field test demonstrates that these parameters can be estimated accurately. Example calculations will be presented to show how the simulator can be used to identify an optimum kill scenario.

Development of Bio-Oil Emulsion to Allow Realistic Testing of Oil Spill Control Equipment

.................................................................................................................................. III Preface..................................................................................................................................... VI Acknowledgement ......................................................................................................... VI Table of

Mathematical and computer modelling reports: Models for petroleum field exploitation

This paper presents some models for an early evaluation of a petroleum field. Based on crude assumptions about a reservior, our models suggest decisions concerning platform capacity, drilling programme and production. We start out with a simple production planning model using linear programming. By mixed integer programming techniques the model is gradually extended. The most sophisticated version of the model can propose platform capacity, where and when wells should be drilled, and the production from the wells. The models are tested on numerical examples, and the results are discussed. From the experiments we conclude that the problems are very hard to solve, and that the size of problems that can be solved is limited by the computational burden. Finally, we give some ideas for future work that may provide better solution methods.