Weighted Frac Fluids for Lower-Surface Treating Pressures

Abstract

Abstract With Gulf of Mexico (GOM) hydrocarbon discoveries reaching record depths and very high bottomhole pressures, the need for proven, weighted fracturing stimulation fluids has become urgent. As previous studies have shown, frac packs have a significant impact in maintaining well productivity in the later production life stages of unconsolidated reservoirs. Thus, sustaining the ability to pump frac packs in these challenging environments is a priority. With conventional frac pack fluids, these greater depths and higher bottomhole pressures often would result in the need for surface treating pressures that exceed the limits of current surface equipment and tubulars. Surface treating pressure can be calculated using the equation: (1) P s = BHTP + P fric − P hyd Ps = surface pressure BHTP = bottomhole treating pressure Pfrict = friction pressure Phyd = hydrostatic pressure The equation shows that an increase in hydrostatic pressure results in a reduction in surface pressure. This is true as long as any corresponding increases in BHTP and friction pressure remain below the hydrostatic increase. If substantial reductions in surface pressure can be achieved, then frac pack treatments remain a safe and viable option in deepwater and ultra-deepwater environments. As of October 2007, sixteen total jobs have been pumped with a weighted frac pack fluid. Of these jobs, eleven treatments have been pumped by Chevron in the deepwater GOM. This paper presents data from these treatments where substantial reductions in surface treating pressures were observed. Also shown is the accuracy to which surface treating pressures with the weighted frac-pack fluid can be predicted.