Fluid type identification in fractured reservoir has always been a worldwide difficult issue. On the one hand, it is very difficult to identify fluid type of fractured reservoir because of its complex lithology, various reservoir types and strong heterogeneity. On the other hand, more and more attention has been paid to fractured reservoir. In this paper, on the basis of the analysis of effect factors, three kinds of method are applied to identify fluid types of fractured reservoir, that is nuclear magnetic resonance (NMR), conventional logging and producing profile method. Theoretical study and applications show that NMR method is effective and reliable in identifying fluid type of fractured reservoir. For conventional logging method, it is recognized that fluid types are closely related with resistivity ratio, clay content and porosity. An identification parameter for fluid type identification(FTI) is therefore proposed integrating the above three elements. FTI close to 0 represents dry layer; it represents oil layer when it close to 1; FTI value of low production layer is between that of dry and oil layer. That production profile is used to distinguish from reservoir fluid is based on that it either can availably observe production nature and oil/water boundary, or can determine output of each formation, especially in the condition of general test. Producing profile method compensates with the previous two methods. These methods were applied to buried hill reservoir of Middle- Upper Proterozoic in Damintun Depression, Liaohe Basin. Obvious geological effect was obtained, and the conformity of identification reaches 88%.
Fluid type identification in fractured reservoir has always been a tough problem in an urgent need to be solved in international well logging industry.
Fractured formation that has reserving nature has different lithology, reserving nature, physical properties, oil-bearing nature and their mutual relations (correlation). Even given the same lithology, the additional four properties are varied substantially under different sedimentary environments. Thus, log characteristics of fractured reservoir vary from one place to another (Keys 1979, Rigby 1980; Sanyal et al 1980, Ouyang et al 1990, Khatchikian 1982). Fractured reservoirs are characterized by complex litholgoy, varied reservoir types, substantial variation of reserving nature and strong heterogeneity, so it much more difficult to identify their fluid types in comparison with conventional reservoirs.
With the rapid development of new well logging technology such as image logging and nuclear magnetic logging, the capacity for detailed logging interpretation of oil and gas bearing reservoirs and formation heterogeneity has been improved to a new level. On the basis of petrophysical study and core scale logging technology and using the logging and geological methods comprehensively, in depth study has been conducted for the fluid type and its distribution pattern under reservoir conditions, which is of great guiding importance for oilfield exploration and development and could promote the technical progress of logging technology and improvement of interpretation level.
