Abstract
Abstract
Fluid loss during workover of subhydrostatic wells is a major concern while servicing the wells in brown/matured fields. Excessive fluid loss results in delayed well activation, formation damage and extra cost due to extra rig days. Loss control by placing a loss control material (LCM) pill has been a well-practiced method to control the fluid loss within desirable limits. However, presence of natural fractures or vugs in the reservoir prevents the formation of filter cake and significantly hampers the performance of these pills. Additionally, heavy use of conventional loss control pills results in formation damage which significantly compromises the productivity of well post workover and requires stimulation job for its restoration. This paper presents a novel self degradable loss control pill consisting of a multi modal distribution of polylactic acid (PLA) in powder, fiber and granular form that is highly effective for plugging/sealing the natural fractures and minimizing the fluid loss. With time and under the downhole conditions, the pill slowly undergoes self degradation and hydrolyze into completely water-soluble products thus minimizing the formation damage. The degradation behavior of the pill has been evaluated and filter cake buildup and aging studies have been performed through core flooding to optimize the particle size distribution of the PLA powder. The filter cake properties have been evaluated through HPHT filter press and results have been compared with the conventional pill. Flow back studies have been carried out to evaluate the cleaning efficiency of pill post activation. Finally, the proportion of PLA powder, fiber and granules has been optimized through fracture plugging studies as per API RP 13I. Application of PLA based LCM pill for loss control during workover is relatively newer concept with limited number of publications describing its intricacies including the loss control material, particle size distribution and pill design. This paper contributes by bridging the existing gaps and providing important guidelines for design and execution of self degradable loss control pill.