Kaiser

SPE 65517
Inflow Analysis and Optimization of Slotted Liners

T.M.V. Kaiser, Noetic Engineering Inc.,
S. Wilson, Marathon Canada Limited, and
L.A. Venning, Regent Control Systems Limited

This paper was prepared for presentation at the 2000 SPE/Petroleum Society of CIM International Conference on Horizontal Well Technology held in Calgary, Alberta, Canada, 6-8 November 2000.

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Abstract

Slotted liners have been used for many years to provide sand control in oil industry applications. They are relatively inexpensive to manufacture and tolerant of installation loads, but historically they have not been able to offer the very small opening sizes of wire-wrap screens for controlling production of fine sands. However, recent advances in slot manufacturing methods provide slot openings that match and surpass the size and tolerance of wire-wrap screens. Furthermore, slotted liners offer an advantage in providing a variable slot density that can be used to optimize inflow or outflow distributions.

In the development of its South Bolney reservoir, Marathon Oil Canada and Noetic Engineering Inc. performed an analytical evaluation of inflow characteristics for a new generation of commercially available slots. Several interesting conclusions were reached, the most significant being that inflow resistance depends much more strongly on slot density than on open area. The inflow characterization was also used to develop an optimized slot density distribution to promote more uniform production over the entire well. The slotting design was incorporated into a new well that was designed to control thermally induced loads, thereby avoiding the sand control characteristics of slotted liner being compromised.

Introduction

Slotted liners are commonly used to provide sand control in unconsolidated heavy-oil reservoirs. The primary factors considered in their design are sand control, inflow resistance and cost. Inflow performance is usually considered to be controlled by the open area exposed to the reservoir, and sand control governed by slot opening size. These become competing considerations in reservoirs with fine sands because slot density must be increased to maintain open area if slot size is reduced to control sand. Furthermore, it is difficult to cut narrow slots, which previously made narrow opening sizes unachievable for slotted liner. Recent developments in slotted liner technology have addressed this last issue, allowing very small slot widths (less than 0.005 in.) with good anti-plugging characteristics to be manufactured economically.

Although small slot-openings are available, their size would demand very high slot density to maintain the open-area targets often specified. The basis for this requirement probably stems from applying channel flow concepts to flow loss through the slots. This basis also leads to the conclusion that fewer, large slots would have less flow resistance than more, small slots for the same open area. However, the basis for such conclusions ignores the most important component of slot-induced flow loss - flow convergence in the sand that packs around the slots. In fact, the flow loss through an open slot is negligible compared with that induced by the flow disturbance associated with the slot.

This paper presents results from a semi-empirical method for evaluating the flow loss due to the flow disturbance created by slotted liners, giving a relationship between slot density and flow loss. This relationship demonstrates that open area is not the best basis for characterizing flow resistance in slotted liners. It can also be used to optimize the slot density over the producing interval to provide a more uniform inflow distribution (or outflow for injection wells).

In the planning stages for new wells at its South Bolney project, Marathon Canada Ltd. pursued a well optimization analysis for the slotted liner. This paper describes the analysis methodology and optimization results. Several liner designs were considered and a sensitivity study of production variations that would result from variations in the controlling parameters is summarized.