Interferometric microseism localization using neighboring fracture

We show how interferometric methods can be used to improve the location of microseismic events when those events come from several different fractures and are observed from a single well. This is the standard setup for a multi‐stage hydraulic fracturing experiment. Traditionally, in such experiments each event is located separately. Here, we adapt the interferometric approach to the problem of locating events relative to one another and show that this reduces the uncertainty in location estimates. To completely recover the Green's function between two events with interferometry requires a 2D array of receivers. When only a single observation well is available, we do not attempt to recover the full Green's function, but instead perform a partial redatuming of the data allowing us to reduce the uncertainty in two of the three components of the event location

Relative event localization in uncertain velocity model

We study a problem of localization of an unknown event location relative to previously located events using a single monitoring array in a monitoring well. It has been shown that using the available information about the previously located events for locating new events is advantageous to localizing each event independently. We compare the performance of two previously proposed localization methods, double-difference and interferometry, in varying signal noise and velocity uncertainty, and propose a framework for selecting the optimal method for a given experiment

Joint location of microseismic events in the presence of velocity uncertainty

The locations of seismic events are used to infer reservoir properties and to guide future production activity, as well as to determine and understand the stress field. Thus, locating seismic events with uncertainty quantification remains an important problem. Using Bayesian analysis, a joint probability density function of all event locations was constructed from prior information about picking errors in kinematic data and explicitly quantified velocity model uncertainty. Simultaneous location of all seismic events captured the absolute event locations and the relative locations of some events with respect to others, along with their associated uncertainties. We found that the influence of an uncertain velocity model on location uncertainty under many realistic scenarios can be significantly reduced by jointly locating events. Many quantities of interest that are estimated from multiple event locations, such as fault sizes and fracture spacing or orientation, can be better estimated in practice using the proposed approach

A unified Bayesian framework for relative microseismic location

We study the problem of determining an unknown microseismic event location relative to previously located events using a single monitoring array in a monitoring well. We show that using the available information about the previously located events for locating new events is advantageous compared to locating each event independently. By analysing confidence regions, we compare the performance of two previously proposed location methods, double-difference and interferometry, for varying signal-to-noise ratio and uncertainty in the velocity model. We show that one method may have an advantage over another depending on the experiment geometry, assumptions about uncertainty in velocity and recorded signal, etc. We propose a unified approach to relative event location that includes double-difference and interferometry as special cases, and is applicable to velocity models and well geometries of arbitrary complexity, producing location estimators that are superior to those of double-difference and interferometry

A unified framework for relative source localization using correlograms

We study the problem of determining an unknown event location relative to previously located events using a single monitoring array in a monitoring well. We show that using the available information about the previously located events for locating new events is advantageous to localizing each event independently. By analyzing confidence regions, we compare the performance of two previously proposed localization methods, double-difference and interferometry, in varying signal noise and velocity uncertainty. We show that the double-difference method combats the signal noise much better due to the averaging over a larger number of travel time measurements. The interferometric method is superior where the main source of error is the velocity uncertainty between the event locations and the monitoring array. We propose a hybrid method that automatically balances these two approaches and produces a location estimator that is superior to either.ConocoPhillips (Firm

Joint microseismic event location with uncertain velocity

We study the problem of the joint location of seismic events using an array of receivers. We show that locating multiple seismic events simultaneously is advantageous compared to the more traditional approaches of locating each event independently. Joint location, by design, includes estimating an uncertainty distribution on the absolute position of the events. From this can be deduced the distribution on the relative position of one event with respect to others. Many quantities of interest, such as fault sizes, fracture spacing or orientation, can be directly estimated from the joint distribution of seismic events. Event relocation methods usually update only the target event, while keeping the reference events fixed. Our joint approach can be used to update the locations of all events simultaneously. The joint approach can also be used in a Bayesian sense as prior information in locating a new event.Massachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Consortium); National Science Foundation (U.S.) (Grant SES-0962484

Bayesian inversion of pressure diffusivity from microseismicity

We have considered the problem of using microseismic data to characterize the flow of injected fluid during hydraulic fracturing. We have developed a simple probabilistic physical model that directly ties the fluid pressure in the subsurface during the injection to observations of induced microseismicity. This tractable model includes key physical parameters that affect fluid pressure, rock failure, and seismic wave propagation. It is also amenable to a rigorous uncertainty quantification analysis of the forward model and the inversion. We have used this probabilistic rock failure model to invert for fluid pressure during injection from synthetically generated microseismicity and to quantify the uncertainty of this inversion. The results of our analysis can be used to assess the effectiveness of microseismic monitoring in a given experiment and even to suggest ways to improve the quality and value of monitoring

Checking up on the neighbors: Quantifying uncertainty in relative event location

With high-permeability hydrocarbon reservoirs exhausting their potential, developing low-permeability reservoirs is becoming of increasing importance. In order to be produced economically, these reservoirs need to be stimulated to increase their permeability. Hydraulic fracturing is a technique used to do this. A mixture of water, additives, and proppants is injected under high pressure into the subsurface; this fluid fractures the rock, creating additional pathways for the oil or gas. Understanding the nature of the resulting fracture system, including the geometry, size, and orientation of individual fractures, as well as the distance from one fracture to the next, is key to answering important practical questions such as: What is the affected reservoir volume? Where should we fracture next? What are the optimal locations for future production wells