Diesel-Based Gel Concentrate Improves Rocky Mountain Region Fracture Treatments

Abstract

More than 500 oil and gas wells in the Denver-Julesburg (D-J) Basin have been successfully stimulated using a water-base fracturing fluid, gelled with a diesel-base gel concentrate. Since the use of this system began in 1985, six different D-J Basin formations, with bottom hole temperatures ranging from 120F to 260F, have been treated. Ammonium chloride and potassium chloride have both been used with the continuously mixed gel to help protect clays. This paper presents a brief description of the chemistry of the system, however, the main emphasis of the paper is toward operational considerations and economics of using diesel-based gel concentrate. The considerations include continuous (on-the-fly) mixing of the gel and an evaluation of ammonium chloride versus potassium chloride for clay protection. Introduction Economic pressures of recent years have motivated the search for more efficient fracturing fluids. New fluids have been developed and existing fluids have been modified to meet the demands of the oil industry. Standard fracturing treatments in the D-J Basin normally vary in size from 1,000 bbl to 5,000 bbl of water. Conventional treatments are premixed jobs, where all the gelling agent is premixed in the frac tanks before any fluid is pumped downhole. The premixing process normally requires a minimum of 30 minutes to mix a 500 bbl tank. Bactericide and buffering chemicals are used to assist in the gelling process and to maintain integrity of the gel until it is pumped downhole. Preparation of fracture fluid from concentrated gel is a process that allows continuous mixing of the gel polymer. As early as 1977, a water-based concentrate was pumped in the D-i Basin, however, limitations in this system prevented it from becoming a viable alternative to pre-mixing. Research continued until 1985, when a hydrocarbon-based concentrate was introduced, permitting continuous mixing of gel with none of the problems presented by the water-based concentrate. In 1986, the addition of a clay control material (ammonium chloride) to the gel concentrate eliminated the need to premix potassium chloride (KCl) in the frac tanks. Only fresh water is placed in the tank. FLUID AND EQUIPMENT DESCRIPTION The concentrate consists of a stabilized polymer slurry (SPS) gel of an intermediate guar or derivatized guar added through an educator to a hydrocarbon, normally diesel. A surfactant and a viscosifying agent are added to stabilize the slurry. The mixture is circulated through a centrifugal pump before the mixture is allowed to stand. Ammonium chloride can also be added to the slurry to assist with formation clay stabilization. The SPS is now ready for use and can be stored or used as desired. To produce the aqueous base fracturing fluid, the gel concentrate must be blended with water utilizing a metering pump and a high shear energy mixing pump. A mobile "pre-gel blender" with a holding tank (80 bbl) is used to help obtain adequate gel hydration before the gel is pumped downhole. The blender tank is divided in half by a weir to prolong hydration time. Hydration rates of field-mixed (1) powdered intermediate guar and (2) liquid intermediate guar are shown in Fig. 1. Laboratory obtained hydration rates show similar responses for both gelling methods, however if field mixing procedures result in fisheyes, lumps, and/or deficiencies a difference such as shown in Fig. 1 may result. Viscosity of the aqueous gel is monitored at the weir. A second observation is made at the centrifugal pump on the job blender and a third viscosity reading is taken from a field rheology loop. P. 493^

Dry-Polymer Blending Eliminates Need for Hydrocarbon Carrier Fluids

“…Until the water-based, liquid-gel concentrates were introduced in 1977 (Yeager et al 1988), fracturing fluids were prepared by mixing dry powder with water on location; this was practiced for many years. Gelling each tank required a minimum of 30 minutes, and a big-volume job (15 to 50 tanks) required numerous chemical floats and gel blenders, and a large spread of pumping equipment.…”

“…Conversion to a diesel-based gel concentrate in 1985 (Yeager and Bailey 1988) reduced the concentrate volume required by a factor of six. A job that required 20,000 gallons of water-based gel concentrate and a 500-bbl frac storage tank could be run out of one 4,000-gal transport of diesel-based concentrate.…”

Viscosity Measurement Throughout Frac Job Gives Increased Gel Control During Continuous Mining

“…7 The acceptance and application of these SPS concentrates has spread rapidly. Others have also reported on their application of SPS materials.a,s,lo Suspension of water soluble solids in oil can be Viscosity Measurement Throughout Frac Job Gives Increased Gel Control During Continuous Mixing 18968…”