Fracture Seismic: Mapping Subsurface Connectivity

Abstract

Fracture seismic is the method for recording and analyzing passive seismic data for mapping the fractures in the subsurface. Fracture seismic is able to map the fractures because of two types of mechanical actions in the fractures. First, in cohesive rock, fractures can emit short duration energy pulses when growing at their tips through opening and shearing. The industrial practice of recording and analyzing these short duration events is commonly called micro-seismic. Second, coupled rock–fracture–fluid interactions take place during earth deformations and this generates signals unique to the fracture’s physical characteristics. This signal appears as harmonic resonance of the entire, fluid-filled fracture. These signals can be initiated by both external and internal changes in local pressure, e.g., a passing seismic wave, tectonic deformations, and injection during a hydraulic well treatment. Fracture seismic is used to map the location, spatial extent, and physical characteristics of fractures. The strongest fracture seismic signals come from connected fluid-pathways. Fracture seismic observations recorded before, during, and after hydraulic stimulations show that such treatments primarily open pre-existing fractures and weak zones in the rocks. Time-lapse fracture seismic methods map the flow of fluids in the rocks and reveal how the reservoir connectivity changes over time. We present examples that support these findings and suggest that the fracture seismic method should become an important exploration, reservoir management, production, and civil safety tool for the subsurface energy industry.

Observational and Critical State Physics Descriptions of Long-Range Flow Structures

“…That flow channelization must be expected in the Earth's crust as the distance of flow increases is thus significant. The fact that flow channels might be mapped by fracture seismic methods, as described by Sicking and Malin (2019) [1], means that, for the first time, the location of the major flow channels at a particular site can be determined and specified in models. The self-similar nature of permeability and the standard deviation of ln permeability from its mean allows the flow-field to be modelled in a statistically realistic way at finer scales.…”

“…Both these distribution and correlation relationships appear to apply just as well along rock formations as across them. (1). Equation (1) can be integrated to yield an expression between the spatial variation of permeability, κ(x,y,z), and the spatial variation of porosity, ϕ (x,y,z) 1.…”

“…As discussed by Sicking and Malin (2019) [1], new methods of passive seismic data acquisition and processing allow ambient subsurface fluid connectivity to be mapped. Complementary to the information on fluid pathways from microearthquakes (MEQ) generated by massive high-pressure (active) fluid injections (e.g., [2]), the new passive technique of Fracture Seismics (FS) can directly reveal both the locations and relative permeabilities of fluid-filled fractures.…”

“…A variety of independent evidence indicates that locations where MEQ and FS activity is most intense are where fluid flow is most likely [1]. FS maps typically reveal long connectivity structures that conduct fluid flow, as illustrated in Figure 1 There are good observation-based theoretical reasons to expect the kind of spatially extended crustal flow connectivity on the hundred-meter scale seen in Figure 1.…”

Physical Modeling of the Krauklis Waves: Insights From Two Experimental Apparatuses

“…The Krauklis wave is a slow wave that can be initiated in a fluid-filled fracture, with a velocity lower than the speed of sound in the fracture fluid . Because the Krauklis wave exists only in fluidfilled fractures, it can provide fundamental information about the fracture size and the fluid involved Sicking and Malin, 2019) suggesting that Krauklis wave analysis can be applied to fracture characterization.…”