Junxiao Li

An effective data processing flow for the acoustic reflection image logging

ABSTRACT Recent studies have revealed the great potential of acoustic reflection logging in detecting near borehole fractures and vugs. The new design of acoustic reflection imaging tool with a closest spacing of 10.6m and a certain degree of phase steering makes it easier to extract the reflection signals from the borehole mode waves. For field applications of the tool, we had developed the corresponding processing software: Acoustic Reflection Imaging. In this paper, we have further developed an effective data processing flow by employing multi‐scale slowness‐time‐coherence for reflection wave extraction and incorporating reverse time migration for imaging complicated subtle structures with the strong effects of borehole environment. Applications of the processing flow to synthetic data of acoustic reflection logging in a fractured formation model and interface model with fluid filled borehole generated by 2D finite difference method, and to the physical modelling data from a laboratory water tank, as well as to the field data from two wells in a western Chinese oil field, demonstrate the validity and capability of our multi‐scale slowness‐time‐coherence and reverse time migration algorithms.

Application of the Reverse Time Migration in Acoustic Reflection Imaging Logging

Reverse time migration (RTM), which has the ability to migrate any type of multiples (surface and internal) to their correct location in the subsurface, can handle multi-pathing, image turning waves and handle steep dips. This paper, for the first time, proposes RTM in the borehole for near borehole structure imaging. In forward simulation of the source wave field and backward extrapolation of the received wave field, the high order staggered grid finite difference method is applied. The cross-correlation imaging condition divided by the receiver illumination is used to get the imaging result. In addition, the differences between RTM in seismic exploration and in the borehole are analyzed, based on which, the RTM is modified to include the borehole environment. Finally, imaging results for the synthetic fracture model and cavity model, as well as real data from both the laboratory water tank and oilfield demonstrate the validity and capability of the modified RTM.

Numerical Simulations for Acoustic Reflection Imaging with FDM and FEM

Acoustic reflection imaging can be applied to detect fractures or interfaces away from the borehole. Although acoustic reflection imaging tools have been available for nearly a decade, some problems still remain. The most difficult are those involved in extracting reflection waves from dominant borehole mode waves, and imaging a complex geologic body exactly. Numerical forward modeling can help us to understand the wave field for acoustic reflection logging, and to verifying the data processing algorithms. In this paper, we report developments in the finite difference method (FDM) and finite element method (FEM) programs to acoustic reflection imaging cases. In particular, the FEM program is employed first to simulate a formation interface and then a fluid-filled fracture outside the fluid-filled borehole model. The FDM is applied in conjunction with an equivalent medium method to simulate the response of fractures outside a borehole. Our results demonstrate that the equivalent medium method can be utilized with the FDM to simulate a fractured formation model effectively. Although the FEM can simulate the reflection logging more accurately, the associated increased computational costs must be justified. For simple models such as linear fractures and interfaces, the FDM may produce a sufficiently accurate result.

On RAI and FDFE Simulations of Acoustic Well Logging Scheme

Numerical simulation can help us to understand the characteristics of the complicated wireline and LWD (Logging While Drilling) acoustic wave fields. The RAI and FEM are commonly used to simulate the acoustic logging wave fields. The former is numerically fast but is difficult to implement for non-axial symmetric models such as tool isolation design and acoustic LWD tool eccentricity. On the other hand, the FEM can be numerically demanding for large 3D models but can handle general spatial variations of elastic properties. This paper extends the application of RAI method to calibrate and associate with Frequency Domain Finite Element (FDFE) method in conjunction with the Perfectly Matched Layer (PML) to simulate the acoustic well logging response in complicated borehole environment. In the RAI method, we have improved the implementation scheme to essentially control the accuracy and to match the geometry of FDFE simulations. The examples to combine the two methods to ensure the correctness of the numerical simulations in complicated wireline and LWD acoustic reflection image are presented.

An Effective Data Processing Flow for the Acoustic Reflection Image Logging

Recent studies have revealed the great potential of acoustic reflection logging in detecting near borehole fractures and vugs. In this paper, we present an effective data processing flow for acoustic reflection image logging by employing a multi-scale slowness-time-coherence method for reflection wave extraction and a Kirchhoff migration for near borehole structure imaging. And the corresponding software has been developed. We first apply the software to process the synthetic data of acoustic reflection logging in a borehole surrounded by interface and fractured formation models generated by a 2D finite difference method (FDM), in conjunction with the equivalent medium model to test the validity of our method and the processing flow. We then apply it to the physical modeling data from a large water tank in laboratory and the field data from two wells in a western oil field of China. As a result, applications of the processing flow to synthetic data, physical modeling data from a laboratory water tank as well as the field data demonstrate the validity and capability of our MSTC, Kirchhoff algorithms and the new-developed software.