ERD campaign for Matrix Acidizing with Coiled Tubing - Nkossa South and Nsoko Fields - Congo

Abstract

Abstract In a field study directed at improved well intervention on horizontal wells, several horizontal wells were treated with acidizing techniques using coiled tubing (CT). The study indicates that CT can be efficiently deployed to target depth in highly deviated and horizontal wells using tools such as vibrators in combination with the effect of a friction reducer and proven pumping techniques. The study emphasizes CT operation design and will provide for operators and services companies common tendencies that may be encountered during those operations. CT mechanical simulations necessary to confirm feasibility of the operation were carried out. However, the complex geometry of the wells led us to identify critical and corrective friction factors after every operation to plan for upcoming interventions - taking into account the technology to be used and well characteristics. Introduction The trend in the E&P industry today is to drill more horizontal and highly deviated wells for several reasons which include accessing reserves in a more economical and more environmentally acceptable way and maximizing the reservoir contact. However, operators are losing the opportunity to effectively perform the required interventions which are normally carried out using CT services such as stimulation, well circulation, and fill cleanout, because of technical limitations. Previous experiences have shown that interventions are limited in terms of reach capabilities in wells located at the edge of the drilling envelope (Fig.1). Several techniques have been developed to counter this limitation, but prediction of the results is difficult and is mainly dependent on a set of external conditions such as completion size and material, production history or well geometry. This document presents a field example of interventions which were accomplished in the Republic of Congo where one of the world's longest CT strings is exploited to intervene in this type of challenging wells (Table 1). Starting from December 2004, Total E&P Congo has used CT intervention to develop the Nkossa South and Nsoko fields (Fig.2) with extended reach drilling (ERD) wells to access extra reserves from the initial platform installed offshore. These interventions have been mainly acid stimulations which were performed immediately after well completion, but also include completion contingencies and perforation operations. The main challenges faced during those operations are:• Well geometry - of ERD wells with measured depth (MD) over true vertical depth (TVD) ratios between 2.02 and 2.70• Chromium completion resulting in high sliding friction factors• Operations carried out from a drilling (tender) barge A critical parameter to the success of many CT operations in horizontal wells is the depth penetration that can be attained before the CT buckles and locks up. Lockup happens when frictional drag forces overcome external pushing forces.