Seismic Imaging of Convective Geothermal Flow Systems to Increase Well Productivity (2020)

A core feature of convective geothermal resource production is wellbore energy flow Q ~ &amp;#x03C1;C x T x V. E.g., for wellbore fluid of volume heat capacity &amp;#x03C1;C ~ 4.3MJ/m&lt;sup&gt;3&lt;/sup&gt;&amp;#x002E;&lt;sup&gt;o&lt;/sup&gt;C, temperature T ~ 230&lt;sup&gt;o&lt;/sup&gt;C, and volumetric flow V ~ 50L/s, wellbore heat energy production is Q~ 50MW&lt;sub&gt;th&lt;/sub&gt; ~ 5MW&lt;sub&gt;e&lt;/sub&gt;. Wellbore fluid flow V =2&amp;#x03C0;r&lt;sub&gt;0&lt;/sub&gt;&amp;#x03D5;v&lt;sub&gt;0&lt;/sub&gt;&amp;#x2113; for open wellbore length &amp;#x2113; is given in turn by the spatially variable product crustal porosity times crustal fluid velocity v &amp;#x2261; &amp;#x03D5;v&lt;sub&gt;0&lt;/sub&gt; at the wellbore radius r&lt;sub&gt;0&lt;/sub&gt;. For a geothermal wellbore to be productive (nominal Q ~ 5MW&lt;sub&gt;e&lt;/sub&gt;), locally variable bulk inflow rates v = &amp;#x03D5;v&lt;sub&gt;0&lt;/sub&gt; across crustal volumes of dimension &amp;#x2113; must be adequate to sustain high wellbore flows (nominal V ~ 50L/s). Wide-ranging crustal well productivity statistics show that few crustal wells flow at these rates. This is not surprising as local bulk flow ~ 10&lt;sup&gt;-2&lt;/sup&gt; m/s needed for production wellbores is decades greater than ambient bulk fluid flow ~ 10&lt;sup&gt;-8&lt;/sup&gt;-10&lt;sup&gt;-7&lt;/sup&gt;m/s characteristic of natural convective geothermal systems. Such rare high flow locales must be found. While existing crustal surveys generally fix resource temperatures T with nominal 500m spatial resolution, as yet no survey technique provides data to locate production-grade flow rates at nominal &amp;#x2113; ~ 50m spatial resolution. In consequence, many costly unproductive wells are drilled before sites of productive local geothermal fluid bulk flow v = &amp;#x03D5;&lt;italic&gt;v&lt;/italic&gt;&lt;sub&gt;0&lt;/sub&gt; ~ 10&lt;sup&gt;-2&lt;/sup&gt; m/s are located. A seismic survey methodology sensitive to crustal flow v = &amp;#x03D5;&lt;italic&gt;v&lt;/italic&gt;&lt;sub&gt;0&lt;/sub&gt; at &amp;#x2113; ~25m resolution has evolved from multi-channel seismic reflection technology applied to the production of shale hydrocarbons. The field-proven seismic flow-imaging methodology can be adapted from sedimentary terrains to volcanic terrains through appropriate seismic refraction means for generating effective seismic velocity models for convective geothermal flow volumes. Numerical simulation for characteristic ambient crustal heterogeneous flow distributions v = &amp;#x03D5;&lt;italic&gt;v&lt;/italic&gt;&lt;sub&gt;0&lt;/sub&gt; at &amp;#x2113; ~50m resolution shows that travel-time data for seismic source energy refracted from deep geothermal wellbores to surface seismic sensor arrays can replicate the multi-channel seismic flow-imaging capability demonstrated for shale formations. Multi-channel seismic reservoir flow monitor detection and mapping of flow-induced seismic emissions in shale formations can be adapted to achieve similar mapping of convective geothermal flow system structures with v = &amp;#x03D5;&lt;italic&gt;v&lt;/italic&gt;&lt;sub&gt;0&lt;/sub&gt; ~ 10&lt;sup&gt;-2&lt;/sup&gt;m/s at nominal &amp;#x2113; ~ 50m resolution. Such seismic emission flow structure maps can greatly reduce the uncertainty and hence the cost of drilling effective production wells at brownfield sites and assessment/development wells at greenfield sites.