Hydraulic Fracture Evaluation Research Articles

Post hydraulic fracturing evaluation and productivity prediction method of fractured tight sandstone gas reservoirs supported by geology-engineering integration

Post hydraulic fracturing evaluation and productivity prediction method of fractured tight sandstone gas reservoirs supported by geology-engineering integration

Elastic-wave evaluation of downhole hydraulic fracturing: Modeling and field applications

We numerically simulate elastic-wave propagation along a fluid-filled borehole with a hydraulically fractured formation. The numerical model is based on the results of hydraulic fracturing on laboratory specimens. Two typical models are simulated: a main fracture crossing the borehole and a fracture network extending from the borehole. In addition, both models contain small, secondary fractures surrounding the borehole. Our result indicates that wave propagation in the main-fracture model is characterized by significant S-wave anisotropy for polarization along and normal to the fracture orientation, with the magnitude of anisotropy depending on the fracture aperture and filling material. In contrast, no significant anisotropy is observed for the fracture network model. In both models, wave propagation is significantly affected by small-fracture-induced near-borehole velocity variation. Our modeling results provide a theoretical foundation for evaluating hydraulic fracturing using the borehole acoustic logging. The hydraulic fracture-induced S-wave anisotropy can be evaluated with the cross-dipole S-wave logging, and the fracturing-induced velocity change can be detected by acoustic traveltime tomography. We used field data examples to demonstrate the effectiveness and practicality of using the borehole acoustic techniques for hydraulic fracturing evaluation.

Through-Casing Hydraulic Fracture Evaluation by Induction Logging II: The Inversion Algorithm and Experimental Validations

Evaluation of hydraulic fractures has been under intensive study since the last decade. Among published works, only a few have included casing effects. This paper focuses on the through-casing electromagnetic (EM) induction imaging method that evaluates hydraulic fractures with enhanced contrasts. An experimental system and an inverse scattering algorithm are presented. The laboratory scaled experimental system is built for the feasibility study of the EM induction imaging method for the through-casing hydraulic fracture evaluation. To develop the inverse scattering algorithm, fractures outside boreholes with metallic casing are modeled by a novel hybrid approximation method. This method combines the distorted Born approximation and the mixed order stabilized bi-conjugate gradient fast Fourier transform method to solve the forward scattering problem. The variational Born iterative method is applied to solve the nonlinear inverse problem iteratively. Experimental results show that the inverse scattering algorithm is effective for EM contrast enhanced through-casing hydraulic fracture evaluation.

Through-Casing Hydraulic Fracture Evaluation by Induction Logging I: An Efficient EM Solver for Fracture Detection

Hydraulic fracturing is an essential way to improve the production of unconventional shale oil and gas. It is important to characterize the produced fractures using either acoustic or electromagnetic (EM) methods. Conventional EM solvers in the low-frequency range face significant challenges by such multiscale problems where the fracture width is orders of magnitude smaller than its diameters. Furthermore, the cased borehole environment is extremely difficult to simulate with conventional EM solvers due to meshing difficulties and the multiscale nature of the problem. In this paper, we develop a hybrid distorted Born approximation and 3-D mixed ordered stabilized biconjugate gradient fast Fourier transform (DBA-BCGS-FFT) method to simulate the very challenging 2-D, 2-D-axisymmetric, and 3-D hydraulic fracture models under both open and cased borehole environments. Numerical examples show that this method has orders of magnitude higher efficiency than the finite element method. The capabilities of the DBA-BCGS-FFT method for the induction tool fracture mapping are demonstrated by comparing with laboratory experimental results and other reference results.

The Applications of BP Neural Network Based on MIV in Hydraulic Fracturing

As a effective stimulation, hydraulic fracturing was commonly used in the mining process of complicated low permeability reservoirs, especially in horizontal shale gas wells more widely. In this paper, we establish the BP (Back Propagation) neural network based on MIV (Mean Impact Value) which is different from traditional BP neural network. We choose the independent variables of training set, plus or minus a certain percentages. Measured by the absolute size of MIV value and analyze the changes of MIV value, we identify the main factors in hydraulic fracturing. Combined qualitative analysis with quantitative calculation, the hydraulic fracturing evaluation model was established. Compared with the traditional BP neural network, the evaluation model shows a high precision, and good stability. Above all, we succeed in achieving a rapid, objective and impartial productivity prediction after hydraulic fracturing in complicated low permeability reservoirs. So in the future, this new hydraulic fracturing evaluation model is about to having abroad applications in the field of hydraulic fracturing.

Pitfalls locating microseismic events from borehole measurements — Practical observations from field applications

Borehole microseismic monitoring of hydraulic fracturing is among the best tools for reservoir stimulation evaluation. After decades of research and execution, the technique has gained a well-deserved place within the engineering toolbox. Moreover, in recent years, its popularity has increased exponentially, together with the development of unconventional resources. However, while involved with a significant number of borehole microseismic monitoring campaigns, I noticed that it is a common practice to overlook fundamental principles during the location of microseismic events. This may lead to potentially erroneous hydraulic fracturing assessments. Examples of microseismic results qualitatively illustrate this assertion showing poor recording, velocity models, processing constraints, and display. They also underscore the interpreter’s role in ensuring the most reasonable outcome from a microseismic hydraulic fracture evaluation. In this respect, any conclusion derived from a microseismic experiment should be fully supported by a thorough understanding of the impact that multiple acquisition and processing assumptions have on the interpretation, as is the case for all other geophysical techniques. Ultimately, my intent is to raise awareness of some common pitfalls while also providing recommendations to increase the value of a microseismic monitoring exercise.

Application of Novel Technologies Helps Unlock Deep Omani Gas

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 152436, ’Application of Novel Technologies Helps Unlock Deep Omani Gas,’ by Andreas Briner, SPE, Joe Curtino, and Hisham Al-Siyabi, Petroleum Development Oman, and Tobias Judd, SPE, Schlumberger, prepared for the 2012 SPE Middle East Unconventional Gas Conference and Exhibition, Abu Dhabi, 23-25 January. The paper has not been peer reviewed. With unique geomechanical, reservoir, and geological properties, some of the large gas-bearing prospects within the Fahud basin in the Sultanate of Oman require innovative drilling and completion practices. A revised drilling and completion workflow, with specific technology deployment and operational flexibility, has been developed in order to account for such reservoir complexity. Introduction Early Paleozoic nonassociated-gas fields operated by Petroleum Development Oman in Oman have traditionally comprised good-reservoir-quality sand-stones located on three- or four-way dip-closed structural highs. While gas-exploration success has continued since 2005, discoveries have been restricted to much poorer reservoirs. Successful continued exploration, appraisal, and further maturation, especially as exploration is also extended into basin-center locations, pose significant challenges given the depth (high temperature and high potential reservoir pressures) and reservoir quality [porosities ranging from less than 3% to 10%, with (ambient) permeabilities ranging from 0.001 to 1 md]. Following a successful completion of a regional basin-evolution and burial history study, a well campaign mainly targeting the Amin-Nimr section in the Fahud Salt basin was designed. The target reservoirs of the Amin formation and Nimr group are Cambro-Ordovician in age and are separated by the Angudan unconformity, estimated to represent a hiatus of up to 20 million years. The Amin and Nimr units are both recognized in the sedimentary basins of north and south Oman, but they have widely differing properties. The Amin formation is a high-net-to-gross-ratio, continental succession deposited in alluvial-/fluvial-fan, sabkha (wet and dry), aeolian, and fluvial sheetflood/sand flat environments, generally with a high water table. The underlying Nimr group comprises two formations, a unit comprising fluvial and lacustrine/playa deposits overlain by a unit comprising large-scale coarsening-upward fluvial deposits. New Operating Model Past reservoir-characterization methods are no longer sufficient when appraising low-permeability gas reservoirs where performance is directly linked to reservoir quality and the effectiveness of the selected method of reservoir stimulation. Several technologies have been applied recently in Oman to improve the understanding of tight gas opportunities, and these include the incorporation of advanced drilling practices; improved understanding of subsurface environment and hydraulic-fracturing design and methodology; hydraulic-fracturing evaluation; and well-completion considerations from a hydraulic-fracturing and subsequent-well-production standpoint.