The Optimum Junction Depth for Multilateral Wells

Abstract

Placement of the multilateral junction is one of the most critical elements in the design of a multilateral well. A misplaced or mal-performing junction can have an adverse effect on an otherwise successful multilateral project. The optimum placement of the junction is a function of reservoir, geological, drilling, and completion criteria. The list may include such criteria as reservoir development strategy, pressures & heterogeneity, geological structure, lithology, wellbore stability, multilateral junction integrity, directional drilling requirements, logging requirements, artificial lift design, and completion type. These combined factors have a direct economic impact on the success and viability of the project. This paper describes a process whereby the proper junction selection criteria can be evaluated in light of pertinent technical and economic criteria and examines lessons learned from case histories with junction problems. Introduction A screening analysis is generally performed prior to having all of the data, offset information, and production information. Consequently, the purpose of this paper is to provide some Rules of Thumb meant primarily to narrow the focus area. Several assumptions are made in the generation of these Rules of Thumb:The beds are assumed to be laminar and horizontal for the base caseDogleg Severity (DLS) is a function of build rate and turn rate. In this paper, the 2D trajectory, where the DLS turn rate component is zero, is considered the base case.Correlations with respect to DLS and equipment capabilities are given with the assumption that the casing exit is from the vertical well.Directional tools, crossflow, formation damage, stimulation, and cleanup are design factors in all multilateral levels. However, discussion of optimal junction placement is primarily focused on TAML Levels 3–6. Levels 1 and 2 have junctions that are typically installed in the same horizontal plane in carbonates or very consolidated sands, where placement is not dependent on a correlation between the type of multilateral system and wellbore geometry. Conventional Well Design Criteria Many of the aspects that are discussed in this paper are not unique to multilateral wells. A cost/benefit analysis will always be performed prior to undertaking any oil field operation; therefore, many of the parameters mentioned are not pertinent just to multilateral well design alone. Issues such as placement of the wellbore in the reservoir, reservoir exposure length, completion and production types are all relevant to conventional well design. The "Morphing" of a Multilateral Well Multilateral wells metamorphose away from the process of conventional well design by creating more options. Instead of one reservoir entry point, it is possible to have two or more. Instead of one set of reservoir conditions, there may be two or more (including fluid types). Target geometries become more convoluted and 3-dimensional, and differences in approach and mindset come to bear with multilateral wells (Figure 1.). Issues Unique to Multilateral Wells The placement and construction of the multilateral junction are the key design differentiators between conventional and multilateral wells, and are the most critical elements in a successful multilateral well project.

Justification of Applying Multilateral Wells in Samotlor Field

“…Key factors controlling the MLT design complexity were structured by literature data [10,[15][16][17]. Therefore, in order to estimate MLT drilling economic attraction in a particular field it is necessary to evaluate the minimum required level of MLT complexity by geologic settings.…”

Justification of Applying Multilateral Wells in Samotlor Field (Russian)

“…По данным литературы [10,[15][16][17] были структурированы ключевые факторы, влияющие на уровень сложности конструкции МЗС. Соответственно, для определения экономической привлекательности бурения МЗС на конкретном месторождении нужно оценить минимально необходимый уровень сложности МЗС по геологическим условиям.…”

Mature Field Re-entries Utilizing Level 4 Multilateral Technology

“…For a level 4 the risk areas include mechanical equipment failure, debris management (metal cuttings), increased cost and complexity (primarily associated with junction construction time, main bore cement quality around junction and lateral cement quality. 3 By using a single packer based hollow whipstock system for all drilling and completion operations the cost and complexity are reduced, as is the construction time. Due to the simplicity of this level 4 system there have been no cases where debris management or equipment failure has been experienced.…”