Yimin Zhao

Hydrocarbon Reservoir Logging Evaluation Methods and Technologies

Logging is an effective method for measuring geophysical parameters of reservoirs based on geophysical properties such as electrochemistry, acoustics and radioactivity. It has been proved that logging is one of the most important and effective technologies for the exploration and evaluation of oil and gas layers. Logging evaluation of reservoirs mainly includes two aspects. One is to ascertain what kind of fluids in reservoirs; the other is to evaluate the quality of oil and gas layers, i.e. the reservoir performance and production capacity. In recent decade, a new generation of logging technology which is represented by imaging logging and nuclear magnetic resonance logging has been formed in order to meet the requirement of exploration and development. These methods play a very important role in the evaluation of complicated lithological reservoirs and the reservoirs with low resistivity, low porosity or low permeability.

Seismic Attribute Analysis

Abstract Seismic attributes are the geometry, kinematics, dynamics, and statistical characteristics of seismic waves, which are extracted or derived from prestack and poststack seismic data by mathematical transformation. For a long time, seismic data only have been used to track lineups of seismic waves in order to delineate the geometry and structural characteristics of oil and gas reservoirs. In fact, there is rich information about lithology, physical properties, and fluid composition hidden in seismic data. As we all know, the characteristics of the seismic signal are caused by petrophysical characteristics and its variability. Geoscientists need to do seismic attribute analyses and calibration in order to eliminate data distortion and dig out lithological and physical properties hidden in seismic data. Especially when people are eager to cognize the heterogeneity of lithological and stratigraphic reservoirs, the rich information about the spatial variability in seismic data seems more precious. In recent years, with the advancement of reservoir interpretation and the needs of three dimensional (3-D) seismic data analysis, scientists have found out more and more new attributes on the basis of conventional seismic attributes. At the same time, methods and means used for the calculation and analysis of seismic attributes are increasing. Seismic attribute analysis has been successfully applied in reservoir lithological prediction, hydrocarbon potential prediction, and reservoir property estimates.

Applicable Scope, Advantages, and Disadvantages of Major Software Packages

This chapter introduces the applicable scope, advantages, and disadvantages of the major software packages used in lithostratigraphic reservoir prediction and evaluation. The functionality of this software includes coherent body, frequency decomposition, 3D visualization, attribute analysis, seismic inversion, hydrocarbon detection, and reservoir evaluation.

Visualization and Spectral Decomposition

The three-dimensional (3D) visualization technique, which appeared in the mid-1980s, is a comprehensive technique that integrates computer data processing and image display, along with many other leading-edge technologies. This technique is used to describe geological phenomena and subsurface characteristics based on their 3D seismic data volume. It can help us describe objective data with real-time processing and display and analyze results effectively with static or dynamic images based on the 3D information. When dealing with large amounts of complex data, this technique helps isolate geophysical information so that geologists, geophysicists, and reservoir engineers can “enter” the data volume and describe and characterize stratigraphic features.

Seismic Coherence Technique

The seismic coherence technique is a remarkably simple yet powerful seismic attribute analysis technique that generates new coherence data and highlights and emphasizes the irrelevance of the seismic data by quantifying the coherence properties of the seismic data. This technique has always been used to interpret discontinuous strata such as faulted beds or/and facies. Typically, it is easy for us to interpret a conventional seismic profile. But it is difficult to interpret vertical profiles that occur along the strike of strata and horizontal slices in the direction of faults that are parallel to phase axes. The coherence body can help us solve these problems. It can accurately delineate the discontinuous characteristics of strata and help us quantitatively interpret faults, lithological bodies, and cavernous carbonate reservoirs. The seismic coherence technique is an important technique for three-dimensional (3D) seismic interpretation and has developed rapidly to become a conventional technique for interpreting faults and lithologies.

Sequence Stratigraphic Research Technology

Sequence stratigraphy is generally used to explain issues of lithofacies interpretation, stratigraphic distribution patterns, and depositional environments based on a genetically related isochronostratigraphic framework. Seismic data, logging information, and outcrop data are all used to build this framework.

Seismic Inversion Techniques

Seismic inversion techniques were developed as a discipline at the same time that seismic technologies were widely applied in oil exploration and development starting in the 1980s. Except for basic theories and principles, seismic inversion techniques are different from traditional seismic exploration methods in geological tasks, involving basic information as well as study approaches. In the early stages of exploration, the geological task of seismic exploration was to find structures and identify traps, and seismic exploration techniques always focused on the ups and downs of reflection interfaces. They mainly relied on the travel time for structural interpretation. The main work of reservoir geophysics is to study the heterogeneity of a reservoir, and the main geological task is to make predictions on the reservoir parameters. Scientists focus on the lateral variation of reservoir characteristics and conduct seismic interpretation based on the information extracted from the results of reservoir seismic inversion.

Exploration Examples of Lithological and Stratigraphic Reservoirs

Lithological and stratigraphic reservoir exploration and production have, through accumulated research achievements and valuable experience, attained many economical benefits over the past 10 years. In this chapter, we primarily introduce the exploration technology of structural-lithologic composite reservoirs in the southern Songliao Basin, carbonate reservoir exploration technology in the Lunnan region, and volcanic reservoir exploration technology in the northern Songliao Basin.

Hydrocarbon Detection Technology

In the past, seismic exploration was used primarily to search for structural traps, but with the advances in seismic acquisition, processing technology, and computer technology, seismic exploration is increasingly used for hydrocarbon detection. Identifying hydrocarbon reservoirs directly on the seismic section has been our goal for many years.

Introduction to Geophysical Exploration Technologies for Lithological and Stratigraphic Reservoirs

In China, oil and gas resources mainly accumulated in the Mesozoic and Cenozoic continental basins, and the proven reserves of oil and gas in continental basins account for three-quarters and nearly half of Chinas total reserves, respectively (Zhai, 1996). After more than half a century of exploration, a large number of structural reservoirs and some lithological and stratigraphic reservoirs were discovered in continental basins. With improved exploration methods, lithological and stratigraphic reservoirs will be the most realistic and promising fields for oil and gas exploration in Chinas mainland for many years into the future.