An Integrated Sand Cleanout System by Employing Jet Pumps

Abstract

Abstract Sand cleanout is operated by circulating a liquid or a multi-phase fluid into the wellbore to bring sand particles to the surface. Although the sand cleanout operations have been applied successfully in most wells with high efficiency and negligible leakage, failure of effective sand removal always occurs in low pressure wells and absorption wells due to heavy loss of circulation. To make the matters worse, solids in the bottomhole may even flow back into the formation to cause further formation damage around the wellbore. In this paper, an integrated sand cleanout system has been developed to effectively remove loose sand particles in low pressure wells and absorption wells by employing a jet pump. More specifically, a high pressure working fluid is pumped through the annulus from the surface and then divided into two parts. One part of the fluid is diverted as the sand carrier fluid to flow downwards, stir up the sand particles via a jetting nozzle at the bottom of a sand cleanout pipe, bring the loose sand particles upwards and then to be boosted by using a jet pump. The other part of the fluid acts as the power fluid of the jet pump to reduce the bottomhole pressure so that the carrier fluid, together with the sand particles, will be sucked into the pump and then lifted to the surface. Detailed structure and principle of the integrated sand cleanout system are described, while a theoretical model is formulated to optimally design the system based on the experimental data and jet pumping theory. It has been shown from field applications that the integrated sand cleanout system makes significant improvements in achieving high efficiency and preventing leakage in low pressure wells and absorption wells. Introduction Increasing interest and efforts have been focused on sand cleanout in the upstream oil and gas industry since the 1960s(1). Although 60% of the oil and gas reserves are discovered in carbonate reservoirs, approximately 90% of the world's oil and gas wells are drilled in sandstone reservoirs, among which 25–35% of the wells experience a certain degree of sand production during the life of the well(2). In principle, sand particles are dragged by the formation fluids, carried out from the formation and settled down at the bottom of the well. By the time the casing is full of the sedimentary solids, the pay zone becomes plugged and the downhole pump gets stuck. Workover activities have to be carried out for reviving the well to bring it back into production(3). Frequently, removal of wellbore fill is considered inadequate, leaving large quantities of fill material (e.g. sand particles) in the well, which often requires repeating well cleanouts in a relatively short time interval. In addition, wellbore cleanouts are extremely time-consuming, preventing timely return of wells to production and increasing the cost of well maintenance(4). Therefore, extensive research efforts have been made to develop:cleanout equipment, such as the concentric pipe, tubing-operated pump-to-surface bailer and coiled tubing with jetting nozzles(5, 6);