Gravel Packing Fluid for HP/HT Environment

摘要

An aqueous-based linear gel composition comprising diutan gum and an environmentally acceptable stabilizer has been developed for gravel packing applications. This aqueous-based gel works at elevated temperatures greater than 300°F. The rheological properties of these linear gels are particularly useful in gravel packing operations that involve shunt tubes. This paper presents laboratory studies that demonstrate the gel's thermal stability, rheological properties, minimal formation damage characteristics, and suitability for gravel packing operations. Linear diutan gels exhibit excellent sand-suspension characteristics, even when they have relatively low viscosity because of their hyper-branched structure. However, their use at temperatures greater than 270°F can be challenging because of limited thermal stability. A new fluid composition that comprises a biodegradable, environmentally acceptable gel stabilizer was developed to address this issue. Thermal stability and rheological properties were studied using a Chandler Engineering~R viscometer at elevated temperatures and various shear rates between 5 and 1021 s~(-1). The sand-suspension characteristic was studied using a high-pressure/high-temperature (HP/HT) autoclave. Formation damage characteristics caused by-fluid invasion were studied by measuring regain permeability after coreflooding. The results show the thermal stability of linear diutan gel improved from 270 to 310°F when the gel stabilizer was added. This fluid was stable up to 4 hours and exhibited excellent shear-rehealing properties at 310°F. The fluid rheology profile at various shear rates is in accordance with the criteria necessary for gravel packing operations that use shunt tubes. The fluid could suspend proppant/sand for 1 hour at 310°F with less than 20% settling. The gel stabilizer helped to improve thermal stability and sand-suspension characteristics by scavenging oxygen dissolved in the fluid and quenching the radicals generated at higher temperatures. The fluid was compatible with completion brine, crude oil, and oil-based drilling mud. Therefore, it could be used in nonaqueous fluid-pack completions. It showed more than 90% regain permeability, which suggests a clean break of gelling agent and low damage to the formation rock. The good thermal stability and sand-suspension properties of the fluid system using the biodegradable, environmentally acceptable gel stabilizer make it a good choice for gravel packing operations in HP/HT reservoirs. The low-residue fluid property helps to ensure economical production rates.