Characterization of permeability fields between horizontal wells using a hybrid of cross-hole imagery and repeat interference test.

摘要

Success of many displacement processes depends on correct estimation of permeability distribution. Among these one could name water flooding, gas injection, and SAGD (Steam assisted gravity Drainage). Traditional formation evaluation techniques rely primarily on shallow investigative tools and measurements. Such data are then correlated using geostatistical-modeling techniques. There is a need for permeability mapping on a broader scale than that offered by local sampling methods.; Using the capabilities offered by horizontal holes, new approaches for characterization of permeability fields can be devised. This study presents new concepts on the use of innovative detection and monitory procedures and the interpretation aspects of such data to map permeability fields between two horizontal or for that matter vertical holes. The study presents a new form of monitoring pressure interference data between two parallel horizontal wells. In pursuit of yet a better reservoir description, this concept is further investigated to include cross-hole tomography data. Spatial correlation length, as an integral part of reservoir characterization, and its influence on both the system effective permeability and pressure responses is also investigated.; Pressure transient variance is used as a stand-alone tool to identify permeability correlation length. A methodology to utilize such a tool is presented in this study.; The proposed conceptual approach for mapping permeability fields is based on integrating the responses at multiple isolated probing points along a horizontal well path, and mapping permeability profiles from the application of a hybrid of deterministic and stochastic models. From this work, it is observed that permeability distribution honoring a given PDF and semi-variograms alone is not conclusive but must be further constrained using data from other techniques such as repeat interference testing. It is also found that variations in pressure, in the observation well, due to permeability contrasts, are captured only during the transient part of the test.; Inclusion of abundantly sampled data, like traveltime tomography, is shown to enhance the estimation of the permeability field. This is done through techniques like ordinary cokriging, which not only recognize the trend of the permeability distribution but also pick up details smeared by other methods.; Discrete wavelet transforms, DWT, is utilized in the appraisal of the system effective permeability, k_eff. It is observed that, with the same PDF of permeability, reservoirs with long correlation lengths, exhibit large values of k_eff whereas reservoirs with short correlation are shown to exhibit low k _eff. This finding was instrumental in quantifying the system correlation length through a type curve.; Finally, the need to characterize and map fractures as flow units is a critical issue in some reservoirs. As part of this study a mathematical model is developed to serve as the base for extending the previous work to include naturally fractured reservoirs.