Remediation of Proppant Flowback-Laboratory and Field Studies

Abstract

Abstract This paper presents the results of laboratory studies and field case histories of a remedial treatment technique using a low-viscosity consolidation fluid system that is placed into the propped fractures by coiled tubing (CT) or jointed pipe coupled with a pressure pulsing tool. The treatment fluids are designed to provide consolidation (for previously placed proppant) near the wellbore to glue the proppant grains in place without damaging the permeability of the proppant pack. Laboratory flow testing indicates that the proppant pack in a fracture model under closure stress only requires low-strength bonds between proppant grains to withstand high production flow rates. The consolidation treatment transforms the loosely packed proppant in the fractures and the formation sand close to the wellbore into a cohesive, consolidated, yet highly permeable pack. Field case histories are presented and the treatment procedures, precautions, and recommendations for implementing the treatment process are discussed. One major advantage of this remedial treatment method is the ability to place the treatment fluid into the propped fractures, regardless of the number of perforation intervals and the length of the perforated intervals without mechanical isolation between the intervals. The fluid placement efficiency of this process makes remediation economically feasible, especially in wells with marginal reserves. Introduction The production rates of many fracture-stimulated wells in the world today are curtailed because of sustained proppant flowback problems. In fact, many wells are actually shut in because operators found them to be uneconomical to produce at subsequently lowered production rates. Typically, production becomes restricted, such as by perforations being covered with produced proppant. The proppant produced during production often causes damage to downhole pumps and to surface equipment. In addition, removing the proppant from the wellbore and repairing the equipment often results in costly downtime for the wells. Low production rates directly affect potential revenue for the operator. Frequent workovers required for cleanup or sand removal, including shut-in time, also factor into the revenue losses caused by proppant flowback or sand infill. However, the problem will return and the loss of revenue will continue to stack up unless a treatment can be found that will remediate the problem at its source and not simply clean up the wellbore. After an initial completion, it is often very difficult to conduct cost-effective remedial treatments to treat proppant production problems. Conventional remedial treatments are usually inadequate without some type of mechanical isolation technique. Conventional methods with a good chance of effective treatment usually either pose too high of a risk for subsequent well problems or are too costly to consider for low-return reservoir conditions (or both). Consolidation fluid treatments have been applied remedially to treat proppant flowback. However, a key problem with using these materials has been an inability to achieve uniform placement of the consolidation fluid treatment into the propped fractures such that the entire perforated interval is adequately treated. This problem is amplified by the presence of variable permeability, perforation debris, formation damage in the near-wellbore region, and the high viscosity of many resin materials. A system that attacks the problem at its source is a better approach to this problem. Using a system of precisely placed treatment fluids into propped fractures conveyed by coiled tubing can turn many marginal wells into excellent producers, and do so cost-effectively. The treatment chemicals introduced into the formation form a consolidated, highly permeable pack that can withstand the high drawdown associated with the production. This paper discusses such a system. Problems of Proppant Flowback As proppant produces out of the fractures along with the produced fluids, fracture conductivity diminishes with time and closure stress as the fracture width decreases, thereby creating a choking effect that causes the potential production of the well to decline. If the produced proppant remains in the wellbore, it may cover the perforation interval, limiting the production flowpath into the wellbore. This process may require a well cleanup to remove the unwanted proppant from the wellbore to re-establish the production from the entire perforated interval.