Classification provides framework for ranking multilateral complexity and well type

Eric Diggins
Shell UK Exploration & Production
Aberdeen

A multilateral classification system, developed by representative industry experts and companies, provides a common framework from which junction complexity and well types can be described and classified.

The Technical Advancement for Multilaterals (TAML) participants held their kick-off meeting in Aberdeen, Mar. 13-14, 1997. The forum's objective was to share worldwide multilateral experiences and provide a more unified direction in the development of multilateral technology.

Advice was solicited from several operators and service companies that provide multilateral equipment and services. Additional information is included from the Breckenridge 1997 SPE Forum Series on multilateral completions.

Because of the wide range of multilateral well complexities, the TAML delegates unanimously agreed that a common classification system would have considerable added value during the planning phase of a multilateral well.

The main benefits include:

Determination of functional requirements-This is one of the key success factors in delivering a well that meets its objectives. A classification system would provide a road map that would allow well and petroleum engineers to efficiently achieve this.

Utilization of the most appropriate system-Followed by the determination of the functional requirements, a classification code would enable the comparison of well requirements and capabilities for the various systems on the market.

Learning transfer-With an increasing number of multilateral wells drilled worldwide, there is a relatively insignificant amount of pertinent offset information. A classification code would enable relevant and accurate comparison of case histories and performance indicators.

At present, there are several multilateral classification matrices in existence, all with fundamental differences. TAML's participants have agreed that the system proposed in this article will supercede all others and that their respective companies will use it in the future (Table 1 [40,969 bytes]).

Matrix explanation

The system is made up of two tiers:

1. Complexity ranking
2. Functionality classification.

The complexity ranking consists of a single numeric character beginning with 1 and ending with 5 ( Fig. 1 [162,158 bytes]). It gives a first-pass indication of the well's complexity, based on junction complexity. In a well with more than one junction, the most complex one is used as the reference.

The functionality classification includes a series of alpha and numeric characters that describe the critical functionality characteristics of the well (Fig. 2 [161,443 bytes]).

Broken down into two sections (well description and junction description), the functionality classification provides additional technical detail of the well. Its primary use is that of a roadmap. It will ascertain the critical requirements during the planning of a multilateral well or describe the status of an existing well.

In a well with more than one junction, each is described, from bottom to top.

Classification code examples

The following examples explain the rankings and descriptions for two multilateral wells.

Example 1: Level 2; ranking N-1-PN-S/2-TR-SEL.

The Level 2 complexity ranking refers to a mother-bore that is cased and cemented with an open lateral (Fig. 1). The N-1-PN-S well description refers to a new well with one junction. It is a producer with natural lift, and it is a single-bore completion positioned above the production packer (Fig. 2).

The junction description 2-TR-SEL refers to a mother-bore that is cased and cemented (Fig.1). It has a through-tubing re-entry with selective flow control (Fig. 3 [153,630 bytes]).

Example 2: Level 5; ranking E-2-IN-D/2-PR-NON/5 (3000psi) -TR-SEP.

The Level 5 complexity ranking refers to pressure integrity at the upper junction, achieved during completion. The E-2-IN-D well description refers to an existing well with two junctions, injector, and a dual-bore completion (Fig. 1).

The lower junction description 2-PR-NON refers to a mother-bore that is cased and cemented with an open lateral. The lower junction is a re-entry achieved by pulling completion with no flow control (Fig. 3).

The upper junction description 5 (3000 psi)-TR-SEP refers to pressure integrity at the junction at 3,000 psi (Fig. 3). It is a through-tubing re-entry with separate production.

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