New Technologies Enhance Efficiency of Hydraulic Fracturing Stimulation in Heavy Oil Reservoirs

Abstract

X oil field was located in eastern China. The lithological component of formation is fine sandstone. The typical characteristics are low-permeability and low-porosity with high viscosity, resin and asphaltene contents, the detail characteristics as follows:1)Shallow buried depth (650~850m); 2)Low permeability and low porosity(the average permeability is 1.0×10−3μm2 and the average porosity is 10%); 3)High oil viscosity,asphalt and wax content (15.2 API,24.3%and17.8%,respectively);4)Ultra-low temperature(45~53°C) with high solidify point(nearly 30°C);5) High content of clay (from 14 to 23%)and high content of velocity-sensitive minerals such as illite, almost 80 percent of wells need hydraulic fracturing treatment, therefore, hydraulic fracturing stimulation is an important technology for this tight heavy oil formations. Over the past two decades, conventional fracturing treatment has far away from satisfaction as a result of high viscosities, poor flow properties and high solidify point in compared to conventional oil. Therefore, a systematic technologies are put forward in this paper, the highlights are:1) Systematic fine formation evaluation prior to fracturing design which contains mineral gradients, nuclear magnetic resonance, rock mechanics, in-situ stress profile, X-CT scanning and so on; 2) A new finely processed pre-pad fluid is developed, and the asphalt and wax content can be reduced through completely miscible between oil and fluid interaction; 3) Low polymer concentration fracturing fluid and variable viscosities are utilized in different treatment stages. The concentration is only 0.2%-0.28% and residue content is 82mg/l reduced 45% and 35% that of the past fracturing fluid,4)Many fracturing treatment parameters are changed such as proppant's type and size, fracturing fluid's type, tip screen-out (TSO)fracturing in order to improve fracture conductivity, liquid nitrogen injection to pad fluid with multi-stage slurry injection schedule, and pumping rate as well, which makes it not only to ensure the successful treatment but also to maximize fracturing treatment potential; 5) Counter measures are applied systematically such as systematic quality control, optimization shut-in time for improve propped profile and flow back, post-treatment management, etc. More than 120 treatments with new technologies in X tight heavy oil field have been performed with encouraging results,95% efficiency with accumulated incremental oil of 110,500 tons and the average post-fracturing rate reach to 10.5m3/d increased more than 50% that of the past well stimulation under the same formation conditions. The novel hydraulic fracturing technology provides a new way to maximize recovery efficiency with in low-permeability heavy oil reservoirs. It also has important strategic significance for development and exploration promotion of these unconventional reservoirs.