Emerging Hydraulic Fracturing Execution Technologies in Unconventional Gas and Tight Oil
Authors: Fonseca Ernesto , Liu Yinghui , Mowad Ben , Gujral Jennifer 
Published: September 2015

The role of technology to improve business results in tight reservoirs is becoming more relevant. As companies continue to grow practical experience in stimulating these reservoirs, the opportunities for technology improvements to fine tune and more accurately optimize also grow. Work showing emerging technologies in hydraulic fracturing (HF) design was presented in 2014 at the International Petroleum Technology Conference (IPTC) in Doha, Qatar [1]. That paper described emerging tools to support low-cost lateral sweet spotting and design opportunities that consider shadow stress modeling. These new capabilities can enable the industry to adopt a more comprehensive HF design strategy, compared to the current standardized, repetitive design approach. These key technologies are briefly reviewed in this paper. As these emerging technologies will soon be commercially available and will create better HF designs, the next step is to focus on technologies that can improve the actual execution of current or more sophisticated designs. This is a key area of opportunity because of the existing inefficiencies shown in the low percentages of contributing fractures in a horizontal well (40 to 75% per internal estimates) and internal estimates of retained fracture propped areas that are very small (half lengths 300 to 500 ft.) compared to the hydraulically created half lengths (2,000 to 3,000 ft.). In a low margin business, reducing these inefficiencies is a significant opportunity for new technology. This paper describes how three new completion technologies hold the promise to improve performance in these two very important areas.

First, the great majority of unconventional hydraulic fracturing treatments today are over-displaced in order to avoid problems in subsequent wireline trips. A new technology called “under-displacement plugs” uses oilfield methods common to cementing, hydraulic fracturing and wireline operations to avoid over-displacement and the resulting partial or total loss of some clusters in a stage. The application of this technology can increase the number of contributing fractures by avoiding over-displacement without increasing the total completion cost.

Second, slickwater hydraulic fracture treatments in unconventional gas and tight oil developments are less expensive and less likely to leave residue than cross-linked gel formulations. However, due to the lower viscosity, proppant transported with slickwater tends to settle out resulting in limited propped height. Polymer coated proppants and high drag proppants are emerging technologies that can increase propped fracture areas: Polymer coated proppants achieve very low settling rates due to the hydration of the polymer coating. When properly formulated and pumped, this improved settling rate can result in larger propped fracture dimensions, in particular increased propped height.High drag proppants achieve lower settling rates by way of their shape and geometry. They are designed in such a way that the center of gravity and centroid of volume do not align in a stable manner, thus proppant particles tumble (flipping end over end) and flutter (spiral side to side like a tree leaf) when settling in a fluid.

Both of these proppants, although made out of sand and ceramic, respectively, have settling rates equivalent to proppants with a specific gravity of 1.5 to 1.8 without the additional expense of lightweight high strength materials or the strength compromise of lightweight materials.

Operational field trials, simulations, and lab data are introduced in this paper to show the potential impact of these technologies and will highlight how their application increases the overall efficiency of these completions. The application of these technologies holds the promise to increase the business performance of tight reservoirs without significant investment increases or radical changes to operational procedures.