RIASSUNTO
Abstract
Economic feasibility studies have shown the need for a low cost, efficient treatment design to make stimulation of the Mancos B formation near Rangely, Colorado practical and attractive. Design simulation indicated that tight control of base gel viscosity combined with a high, but achievable, rate of displacement was necessary. This would place a 40 lb linear gel system containing 73,000 lb proppant in the formation at a rate of 50 bbl/min.
Operational efficiency from the personnel and equipment involved could best be attained through use of a continuous-mix approach since job time was short and rig-up time and expense would be greater in a batch mix scheme.
When treating wells with low viscosity linear frac gels, real-time information about frac fluid viscosity is critical, especially when using continuous mix fluid systems to stimulate shallow formations. Pipe transit time is on the order of 30-45 seconds; therefore it was essential that the fluid had developed significant viscosity to effectively create a fracture of sufficient height and width to place proppant throughout the net pay zone. proppant throughout the net pay zone. A monitoring system consisting of a rheology skid, two viscometers, and data acquisition hardware has been combined with a stabilized polymer system (SPS) to deliver a controlled, continuously-mixed linear fluid system. Viscosity was measured at three critical points in the flow stream. points in the flow stream. From this work it has been observed that laboratory measurements are comparable to those obtained using field equipment to mix job-sized volumes of fluid. This paper presents a comparison of the laboratory findings and field results. Also presented are design details of the setup, job designs, and a discussion of the continuous mix system.
Introduction
A planned 28-well fracturing program sought to place a 40 lb/Mgal linear gel system commingled with carbon dioxide (CO2) at a high rate. Pipe transit time was about 30 seconds, so precise viscosity control and reliable performance of the gel were considered to be critical elements of the planning process.
The adaptation of SPS to follow an efficient quality control and monitoring program for stimulation treatments was necessary. This was accomplished as indicated in the job procedure listed in Table 1.
A main concern was quality control throughout the entire treatment. The viscous polymer gels produced from concentrates were, therefore, monitored at several points along the path to the wellhead at specified volume intervals throughout the job. Delivery of a fluid with viscosity of 28-34 cp was desired. This became the goal of SPS performance. The use of two model 34 Fann viscometers, both equipped with a specially designed flow-through cup, as well as a flow loop rheology skid, previously described elsewhere, were used in this quality control procedure.
SPS concentrates were first introduced into oilfield applications July, 1978 by Briscoe, et al. These were inhibited, aqueous-based slurries that contained KC1 as a clay protection additive. They remain in routine use today. Aqueous concentrates can suspend a limited quantity of polymer (ca 0.7 lb/gal) due to the physical swelling and viscosification that occurs in a physical swelling and viscosification that occurs in a water-based medium. Higher quantities (up to 5 lb/gal) of solids can be suspended in a diesel fuel carrier fluid. This fact and a desire for greater efficiency of equipment use led to the development of diesel-based SPS concentrates. These were first used in 1985. The acceptance and application of these SPS concentrates has spread rapidly. Others have also reported on their application of SPS materials.
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