Characteristics of Clay-Abundant Shale Formations: Use of CO2 for Production Enhancement

Abstract

Clay-abundant shale formations are quite common worldwide shale plays. This particular type of shale play has unique physico-chemical characteristics and therefore responds uniquely to the gas storage and production process. Clay minerals have huge surface areas due to prevailing laminated structures, and the deficiency in positive charges in the combination of tetrahedral and octahedral sheets in clay minerals produces strong cation exchange capacities (CECs), all of which factors create huge gas storage capacity in clay-abundant shale formations. However, the existence of large amounts of tiny clay particles separates the contacts between quartz particles, weakening the shale formation and enhancing its ductile properties. Furthermore, clay minerals' strong affinity for water causes clay-abundant shale formations to have large water contents and therefore reduced gas storage capacities. Clay-water interactions also create significant swelling in shale formations. All of these facts reduce the productivity of these formations. The critical influences of clay mineral-water interaction on the productivity of this particular type of shale plays indicates the inappropriateness of using traditional types of water-based fracturing fluids for production enhancement. Non-water-based fracturing fluids are therefore preferred, and CO 2 is preferable due to its many unique favourable characteristics, including its minor swelling effect, its ability to create long and narrow fractures at low breakdown pressures due to its ultralow viscosity, its contribution to the mitigation of the greenhouse gas effect, rapid clean-up and easy residual water removal capability. The aim of this paper is to obtain comprehensive knowledge of utilizing appropriate production enhancement techniques in clay-abundant shale formations based on a thorough literature review.

Impact of shale on properties and oil recovery potential of sandstone formation for low‐salinity waterflooding applications

“…With increasing shale content, the porosity of sand‐packs decreased and reached the minimum level of 26% for SP‐6 exhibiting 75% sand and 25% shale (Table ). Our results indicate that shale's inclusion has caused a marked decrease in the porosity of sand‐pack, which was also demonstrated by Zhang et al, who concluded that the impact of increased swelling in shale is connected with blockage of free space in porous formations that in turn probably makes the sand‐pack less porous and decreases porosity. Thus, the shale, made up of primarily fine grains, occupies the interstitial space inside the sand‐pack during mixing and ramming.…”

A Multi-Parameter Optimization Model for the Evaluation of Shale Gas Recovery Enhancement

“…The commercial development of shale gas has been driven by three key advances in technology and science: (1) horizontal well plus multi-stage hydraulic fracturing [1][2][3][4][5][6], (2) the understanding of gas storage mechanisms [1], and (3) the understanding of multi-scale mechanisms of gas flows from shale matrix to hydraulic fracture [7][8][9][10]. A shale gas reservoir has free gas stored in matrix pores and natural fractures, and adsorbed gas on the organic matter [11,12].…”

Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

“…Therefore, an understanding of the total fracturing fluid leak-off rate is one of the most important indices in fracturing design using CO 2 , especially in relation to the total volume or weight of fracturing fluids. The permeability of shale matrix to water is valued 22.10 nD which is measured in Section 5 at 16 MPa injection pressure, and the permeability to liquid CO 2 is valued at the same injection pressure at room temperature, according to Equations (7) and (8), the ratio of the leak-off rate in volume of CO 2 and water is around 14.03, and the ratio in weight is around 12.62. With the increase of penetration distance, the penetration distance of CO 2 is much higher than that of water due to lower viscosity, and a lower pressure gradient for CO 2 injection can reduce its leak-off rate, which indicates that the ratio of the leak-off rate between CO 2 and water is over-valued.…”

“…The imbibition of water into the shale matrix easily causes a blocking effect in tiny pore throats, which closes the channels for gas transport from the shale matrix to the created fractures [6]. The formation damage caused by injected water is more serious in clay-abundant shale formations, because the interaction between water and clay minerals can induce the swelling of clay minerals, which further reduces the porosity of pores and fractures [7]. In the light of other environmental concerns caused by water-based fracturing fluids, such as large water consumption and wastewater generation [8], hydraulic fracturing have been banned legislatively in some countries [9].…”