Liangjun Yan

Field trials of LOTEM in a very rugged area

Geophysical surveys are difficult to carry out in southern China because the surface is covered by limestone, the geology is complicated, and the topography rugged. Conventional seismic methods are often less than satisfactory because the high‐velocity surface layer and great velocity variation in the subsurface.

Array TEM Sounding and Application for Reservoir Monitoring

Summary Theoretical and numerical modeling results show the feasibility of residual oil mapping and d ynamic monitoring of steam or water driven reservoirs by using the electric source TEM method. A pilot survey of customized array TEM was carried out over a steam driven heavy oil reservoir. Field results confirm that the resistivity anomalies are well correlated with residual oil saturation.

Model study on through casing time domain electromagnetic (TEM) probing

Analytical and numerical solutions of time domain electromagnetic responses of earth model with axis symmetry have been derived and model responses have been calculated with a pulse source stimulating inside metal casing. Anomalous pattern of TEM responses varying with casing parameters (thickness, conductivity and magnetic permeability) and sensitivity to resistivity changes of formation outside of casing were analyzed. Model results have shown that through casing TEM sounding is feasible and has advantages of multi-components, multi-parameters, deep and untouched probing.

Continuous TDEM for monitoring shale hydraulic fracturing

Monitoring and delineating the spatial distribution of shale fracturing is fundamentally important to shale gas production. Standard monitoring methods, such as time-lapse seismic, cross-well seismic and micro-seismic methods, are expensive, timeconsuming, and do not show the changes in the formation with time. The resistivities of hydraulic fracturing fluid and reservoir rocks were measured. The results suggest that the injection fluid and consequently the injected reservoir are characterized by very low resistivity and high chargeability. This allows using of the controlled-source electromagnetic method (CSEM) to monitor shale gas hydraulic fracturing. Based on the geoelectrical model which was proposed according to the well-log and seismic data in the test area the change rule of the reacted electrical field was studied to account for the change of shale resistivity, and then the normalized residual resistivity method for time lapse processing was given. The time-domain electromagnetic method (TDEM) was used to continuously monitor the shale gas fracturing at the Fulin shale gas field in southern China. A high-power transmitter and multi-channel transient electromagnetic receiver array were adopted. 9 h time series of Ex component of 224 sites which were laid out on the surface and over three fracturing stages of a horizontal well at 2800 m depth was recorded. After data processing and calculation of the normalized resistivity residuals, the changes in the Ex signal were determined and a dynamic 3D image of the change in resistivity was constructed. This allows modeling the spatial distribution of the fracturing fluid. The model results suggest that TDEM is promising for monitoring hydraulic fracturing of shale.

The Petrophysical Study for Shale Sample Based on Autoscan-II Platform

Petrophysical study is playing an important role in oil and gas exploration. Shale gas and shale oil is blooming in recent years in many countries. Less rock physics knowledge is known about shale relatively to other rock type such as sandstone and limestone. In this paper, we carried out a rock physical study of shale core sample which is drilled from north China. The plan distribution of permeability, P wave velocity, S wave velocity and complex resistivity were acquired based on AutoScan-IIplatform. The results show that the permeability of the shale sample is basically low with values of 0.1 to several micro Darcy (mD) except some fracture areas in the surface, which has values of about several tens mD. The permeability can basically describe the distribution of the fracture. The complex resistivity has the similar characteristics with permeability, which is also roughly corresponding to the position of the facture. As for the Vp and Vs, although not very good correspondence with the surface, they are still approximately present the high and low velocity feature of the core sample as well. This result is significantly helpful for shale gas exploration and production.

Forward Simulation Results of CSAMT Data on Considering IP Effect

The CSAMT responses of geoelectric media are actually the accumulation of electromagnetic response and induced polarization under the stimulation of controlled source. The resistivity is dealt as a parameter which is scarcely related to the frequency when we proceed the forward and inversion with field data. Due to the induced polarization of underground layers, however, the resistivity of polarized layers is complex number relating to the frequencies and using only resistivity will lead an inaccurate result. This paper provides a primary trial in solving this problem that not only the current research situation of basic theory of IP in recent years, but also a few of preliminary modeling results are presented

Electromagnetic Methods for Shale Gas Exploration in Southern China

The shale gas is becoming a new strategic energy source in the world. To improving the efficiency of exploration and production of such a non-conventional resource has been a global choice of oil and gas powers. Many previous researches have revealed that China has equivalent amount of shale gas reserves as USA. China-based research has shown that the southern China is one of the most potential areas for shale gas exploration. However, the complex topography with carbonate covers and sophisticated geological structures in southern China is a main difficulty for seismic exploration to get reliable and high-resolution data. This paper alternatively present electromagnetic exploration methods that are applicable to shale gas exploration in such rugged area.

Complex Resistivity Method and its Application in Mineral Resource Exploration

Complex resistivity (CR) is one of an electromagnetic method which plays an important role in the exploration of oil and gas, underground water as well as solid mineral resources in recent years. Nowadays China is under fast developing and there is still a big gap between the supply and demand of mineral resources. As an effective controlled source electromagnetic method, CR method can be easily used to judge the content of resources, determine the target reservoir and select a favorable drilling area. In this paper, an introduction to CR method and its application in copper mine exploration in west China is present. The result shows that CR is an effective electromagnetic method in the exploration of deep mineral resources.

Near Surface Velocity Investigation With STEM and Its Application On The Static Correction For Seismic Data

SUMMARY Due to the rugged topography and the complexity of near surface in the Tianshan mountain frontier of western China, difficulties have been encountered in the seismic static correction. One of the effective methods, Shallow transient electromagnetic sounding(STEM), has been used in the seismic static correction since the beginning of this century. Contrasting the resistivity curves inverted from STEM to the stratum velocity curves observed by micro-logging at the same sites showed that the coherence of the shallow structure of stratum velocity and the layered resistivity was perfect, and the relationship between stratum velocity and resistivity was very complicated. Based on the Faust formula, the modified method in which the stratum velocity was described as a polynomial function of resistivity and depth in logarithm domain was put forward. By using the stratum velocity from micro-logging and the resistivity from STEM the coefficients were calculated with conjugate gradient method, so the experiential formula of stratum velocity as a function of resistivity and depth was determined, with this formula the stratum velocity was imaged upon the resistivity profile. The result was important and valuable to the identification of the low velocity boundary, and also was possible to the establishment of near surface velocity model for seismic static correction. The resolution of seismic profile after the static correction with velocity model given by STEM was higher than that given by micro-logging.

Quadratic Function Approaching Method For Magnetotelluric Sounding Data Inversion

Quadratic Function Approaching Method for Magnetotelluric Sounding Data Inversion Liangjun Yan* and Wenbao Hu, Department of Geophysics and Petroleum Resources, Yangtze University, Keni Zhang, Lawrence Berkeley National Laboratory Summary The quadratic function approaching method (QFAM) is introduced for magnetotelluric sounding (MT) data inversion. The method takes the advantage of that quadratic function has single extreme value, which avoids leading to an inversion solution for local minimum and ensures the solution for global minimization of an objective function. The method does not need calculation of sensitivity matrix and not require a strict initial earth model. Examples for synthetic data and field measurement data indicate that the proposed inversion method is effective. Introduction Most well-known approaches for MT data non-linear inversion, such as Newton’s method and conjugate gradients-based methods, are based on an objective function (Φ(m)) approximated with its first-order Taylor expansion about the reference model (m k ). This is because that the objective function in the vicinity of extreme point can be approximated by a quadratic function. Inversion problems in geophysics do not search for the extreme value of objective function, but the minimum value or global extreme value of it. However, most MT inversion algorithms, such as OCCAM (deGroot-Hedlin and Constable, 1990), RRI (Smith and Booker, 1991) and NLCG (Rodi and Mackie, 2001), are limited to solving for the “extreme” value. These nonlinear inversion methods use partial differentiation information (Jacobian matrix) to determine the iteration search direction, which may lead to a solution for local minimization. Computation of Jacobian matrix is time consuming and limits the speed of MT data inversion. In this paper, the quadratic function approaching method (QFAM) is applied to the inversion of one- dimensional MT data. The QFAM method is originally used in the non-linear optimization study. This approach avoids the calculation of gradient or second order derivative by using the function value only, and does not need calculation of sensitivity matrix which greatly simplifies the inversion procedure. Additionally, the proposed method does not require a strict initial earth model. Theory The QFAM is implemented by constructing a quadratic function through several control points in the model space. At the control points, quadratic function is given the same value as the corresponding objective function. The minimum of objective function is approximated by minimum value of the quadratic function. An optimization algorithm developed by Zhao (2000) for searching control points is used to update quadratic function and improve the determination of minimum location. An iterative procedure is followed until the optimized global minimum point has been reached. The solution is considered to be the best approximation of the real earth model. Objective Function MT data and earth model has a very complex nonlinear relationship. We can write the inverse problem (N layers) as d = F ( m ) + e , where d is a data vector [d 1 , d 2 , …, d N ], m is a model vector, m=[m 1 ,m 2 ,⋅⋅⋅,m N ], e is an error vector, and F(m) is a forward modeling function. In this study, log values for the data vector and model vector are used. Inverse problems in geophysics are undetermined. We find a specific model by minimizing a model objective function subject to data constraints. In an iterative inverse procedure, it is not enough by only matching field measured data. The matching approach may lead to a very complex earth model, or a false structure. One of the effective approaches for reducing uncertainty of inversion is by defining an objective function with parameters of the model structure, and the inverse problem is solved by minimizing the model objective function subject to adequately fitting data. We solve the problem following Tikhonov and Arsenin (1977), taking a regularized solution to be a model minimizing an objective function, Φ, defined by Φ ( m ) = ( d − F ( m )) T V − 1 ( d − F ( m )) + λ m T L T Lm (2) where λ is regularization factor and a positive number. The positive-definite matrix V plays the role of the variance of the error vector e. The second term of equation (2) defines a stabilizing functional on the model space. The matrix L is a second-difference operator. For a flattest model norm matrix L, we adopt the equations by Routh and Oldenburg In solving inverse problem, the earth model is discretized into 30-40 layers in a constant layer thickness (in log