Justifying Use of Multilateral Wells in the Samotlor Field
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 136085, ’Justification of Applying Multilateral Wells in the Samotlor Field,’ by A.F. Sunagatullin, SPE, A.V. Arzhilovskiy, T.F. Manapov, SPE, and Y.V. Mikheev, TNK-BP, prepared for the 2010 SPE Russian Oil & Gas Technical Conference and Exhibition, Moscow, 26-28 October. The paper has not been peer reviewed.
A feasibility study was performed for drilling multilateral wells (MWs) in the Samotlor field. The main objectives were to increase reservoir sweep and improve drilling economics. To select priority targets, a ranking was made through expert evaluation. The feasibility study was conducted on development targets by use of sector dynamic models. Minimal required levels of MW-design complexity were chosen for economic evaluation.
Introduction
The Samotlor field is in the Nizhnevartovsk district, Russia. It has been on production for more than 40 years and includes 11 development targets. Reservoirs occur at 1500 to 2500 m and, essentially, differ by properties. To sustain production levels, implemented technologies include hydraulic fracturing with controlled fracture development, flow-deviation techniques, horizontal wells (HWs) with multiple fractures, and variable drilling profiles. A promising technology is drilling of MWs.
The feasibility study was a complicated, comprehensive task that required examining three equally important interacting aspects: subsurface, MW design and drilling, and project economics. It was necessary to show the project’s value in absolute and relative performance under conditions of uncertainty at an early evaluation stage. Key questions included the following.
Where to drill MWs (field/formation, unit/zone, and with what parameters)?
How much greater is MW production than that with other well types for various reservoir parameters?
What well-design-complexity level should be selected?
In this study, the reservoirs were ranked by use of expert evaluation. An evaluation and comparison of technical performance parameters (e.g., cumulative production) between MWs, HWs, and vertical wells (VWs) were made for the two highest-priority targets. The best zones for MW drilling were defined by modeling. Next, factors affecting well-design complexity were structured, and the most-probable complexity level for each reservoir was determined. Then, economic criteria were proposed, accounting for reservoir complexity and depth, to evaluate against other fields.
Subsurface
The main tasks from the subsurface aspect were estimating the MW technical-performance indicators and comparing different options for field development. It was necessary to select formations with the highest potential benefit from MW technology. The main geologic criteria were defined from a literature review of applying MW technology in all regions of the world. By use of the criteria, an expert-evaluation system was created that ranked fields and formation units by MW applicability. The criteria were picked in such a way as to highlight reservoirs in which MWs provided relative advantage vs. single wellbores. Criteria included viscosity, permeability, reservoir depth, net oil-pay thickness, remaining reserves, and presence or absence of an aquifer or gas cap.