Passive seismic imaging for real time management and verification of hydraulic fracturing and of geologic containment of hazardous wastes injected into hydraulic fractures

A work station device for real time passive seismic imaging and management of disposal of hazardous wastes by injection into subterranean hydraulic fractures with verification of geologic containment, comprising:

• a. Means for arranging and installing an array of high sensitivity, high resolution seismic sensors about a selected subterranean injection zone and disposal well for injection disposal of hazardous wastes;
• wherein said sensors are installed in boreholes, drilled to a selected depth;
• wherein said sensors provide known observation points for maximum practical coverage of said injection zone;
• wherein said sensors comprise means for detecting and receiving passive seismic signals from microearthquake events in said expected injection zone as described in step g. below;
• and making precise measurement of location coordinates of said sensor observation points;
• b. Means for connecting said sensors to a computer-based, real time, automatic seismic data processing system:
• 1. wherein said computer-based system comprises means for automatic processing of passive seismic signal data, on real time basis, continuously during and throughout planned fracture processing at a given site for periods which may last as long as several months;
• and
• 2. wherein said computer-based system further comprises means for real time compression of passive seismic signal data, simultaneously receiving, recognizing, recording and processing continuously, signal data from as many as 50 channels or more of data at rates of 2,000 signals per second, per sensor, or greater, and for detecting, flagging, and recording precise measurements of arrival times of both primary and secondary wave phases of passive seismic signals on a real time basis as received, with only signal segments retained for further processing;
• c. Means for determining precise velocities of seismic signals traveling through underground strata in and above said injection zone, wherein said determination comprises measuring origin times and arrival times of signals generated by perforation of said well by means well known in the art, as said signals travel from known location of said perforation to said known sensor observation points;
• d. Means for calibrating a best seismic velocity distribution model of said strata, wherein said calibration comprises the steps of:
• (1) making static corrections to observed seismic event arrival times to account for model bias;
• (2) calculating theoretical hypocenter locations using hypocenter location routine from step 1. below, and a range of hypothetical velocities;
• (3) comparing said theoretical locations with known locations of said perforation shots;
• and
• (4) selecting best velocity distribution model which gives calculated locations which are closest to known shot locations;
• e. Means for pumping and injecting a slurry suitable for hydraulic fracturing and injection, comprising said hazardous wastes mixed with a selected liquid transport agent, wherein said slurry is injected through said perforation at pressures exceeding minimum principle stress of formations of said injection zone to cause controlled fracturization wherein hydraulic fractures are created in said formation which grow and propagate as additional slurry is injected;
• and continuing to inject said slurry into fractures as generated in surrounding rock formation at controlled rates while monitoring and controlling down-hole pressure and flow rates to ensure efficient and complete disposal of required volume of said hazardous wastes;
• f. Wherein said injecting and fracturization causes changes in local geologic effective stresses which trigger microearthquakes;
• wherein said microearthquakes at the instant of fracture trigger weak passive seismic signals from the source of each said microearthquake event;
• wherein said passive seismic signals travel through said formations to said array of sensors;
• and wherein the sources of said signals are known to be located within and acceptably close to said induced hydraulic fractures clustering in narrow ellipsoidal volume of rock which enclose said induced fracture or network of fractures;
• g. Means for receiving said passive seismic signals, at each said sensor;
• converting them to analog electrical signals;
• and transmitting them as received to said processing system;
• h. Means for amplifying and digitizing said analog signals, wherein a separate channel of data is produced from each sensor;
• i. Means for automatically detecting, measuring, and recording said digital data using real time signal detection algorithm:
• 1. wherein, whenever the signal energy level of a channel exceeds the background noise level by a preset ratio, a signal is recognized and declared;
• and
• 2. wherein arrival time and amplitude of said signal are measured and recorded;
• j. Means for determining and recording, on real time basis, which signals and arrival times are associated from the same microearthquake event, based on said known station locations and velocities in an association algorithm;
• k. Means for sorting and identifying said associated signals for real time, positive identification and recording of their phase types, which may be either primary waves or secondary waves;
• and recording precise arrival times of said primary and secondary waves at each of said sensors;
• l. Means for determining hypocenter location and origin time for signals from each said microearthquake event in real time as said events occur, based on existing known earthquake hypocenter location program and hypocenter location data;
• m. Means for recording said resulting hypocenter location and origin time for each said microevent to an event list in real time, wherein said list is continually updated with new location and origin time of each said microearthquake as said events occur;
• n. Means for automatically calculating moment tensor source mechanisms for each event, based on said signal amplitudes for each said event;
• determining if said event has a tensional source, which indicates it is part of the hydraulic fracture, or a shear source, which indicates it is adjacent to but not in the hydraulic fracture and thus contains no waste slurry;
• and recording each said tension source by type and location;
• o. Means for determining orientation azimuth of the microfracture plane associated with each said event based on said moment tensors;
• p. Means for creating and displaying an animated visualization image, using computer codes and said real time event locations, source mechanisms and orientations, wherein said visualization image comprises:
• 1. displaying a rotatable, animated, three dimensional, real time, visualization of said hypocenter event distributions, wherein a distinction is made between hypocenter locations based on said source mechanisms;
• wherein said animated visualization is provided with high resolution subject only to small and acceptable deviation of said source locations;
• 2. animating said visualization in real time;
• 3. accurately imaging and visually displaying development, growth, propagation, direction and velocity of induced fractures in real time as said injection process continues;
• 4. displaying said animated map visualization on large screen television for viewing by environmental officials and hydraulic fracture technicians;
• 5. rotating said three dimensional display on said screen as desired to show any desired cross section and map view;
• 6. displaying predicted fracture geometry and comparing it with current actual geometry as displayed in real time during said injection process;
• wherein said predicted fracture geometry is constantly updated on a real time basis to provide continuing updated prediction and model of future growth;
• and
• 7. visualizing said fracture growth in real time displayed within a realistic, real time animated image of the local geology, in spatial relationship to other geologic formations, zones, reservoirs, wells, fractures and sources of potable water, and simultaneously providing the observer with continuously updated visual image and display of data concerning the properties of the disposal operation including pressure, slurry volume, flow rate, viscosity, and the like, as injection continues;
• q. Means for depicting and displaying said tensional and shear events with different colors or symbols in said animated map visualizations:
• 1. wherein the areal extent of said displayed sources provides real time demonstration of the location and extent of waste filled fractures;
• 2. wherein said animated map provides real time verification that said fracture is contained in said selected injection zone;
• and
• 3. wherein the direction and velocity of any migration of seismic activity toward said sensitive zones is immediately evident, permitting management decisions and actions such as shut down or modification of injection flow rates and pressures to be accomplished long before said sensitive zones are threatened;
• and
• r. Means for integrating said data installing, receiving, acquisition, compression, processing, calculating, determining and visualization means into a modularized work station system for in-process management and control of hydraulic fracture treatments and for verification of geologic containment of hazardous wastes injected in hydraulic fractures.