Abstract

Multilateral well technology has been deployed in different parts of the world. The main motivations for drilling multilateral wells are, to increase drainage area which improves hydrocarbon recovery and then to minimize the cost by sharing the motherbore. South Pars gas field is located in Persian Gulf and is known as the largest gas field in the world; this field is extended into the Qatar territorial water where it is called the North Field. The reservoir in South Pars field includes four producing layers, K1, K2, K3 and K4; the ordinary trajectory of wells in this field is a 42 degree slant path that touches all of these layers and it culminates in a commingled production after all. But problem arises here, on the flanks, where the level of WGC is too high that K3 and K4 are inundated with water and there is no enough production from two other layers then it calls for finding another way to extend the production period. In this case the role of multilateral wells becomes highlighted and those conventional wells can be substituted by their novel multilateral forms. In this study, a bi-lateral well was designed using offset well data and related software. The design includes different drilling and completion options. In the next step the cost of this well was estimated. A full field reservoir simulation model was implemented in order to investigate the gas production improvement of the proposed well. Finally it turned out that, though the drilling cost of the bi-lateral well was increased by 37% in comparison with the original monobore well, the total gas production will be improved by 40%.

Introduction

South Pars gas field is located in Persian Gulf and known as the largest gas field in the world, which is extended into Qatar territorial water where it is called the North Field. It consists of four producing gas layers K1, K2, K3 and K4 which are separated by anhydrite layers. The ordinary trajectory that mostly is deployed in this field is a 42 degree deviated path which enters the reservoir and passes through K1, K2, K3 and K4 and results in a comingled production from these four layers. In the satisfying condition this type of trajectory seems to be the most economical one owing to increasing the exposed area of the well bore to reservoir and also decreasing the drilling measure depth. The problem arises here, on the flanks where the level of WGC is too high that the pay zone only consists of K1 and K2, the production period is too short to suffice us, and then drilling conventional monobore wells is not a wise choice (Figure 1). As a consequence drilling multilateral wells in this situation can be the best option in order to dig out of difficulties. In the following part a drilling program is proposed roughly for such a multilateral well.

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