The Application Of High Resolution Sequence Stratigraphy And Log Evaluation In Subtle Reservoirs

With the discovery of subtle reservoirs, the prospecting theory and technique for subtle reservoirs and resource evaluation technology have been largely improved. Of all the research methods about subtle reservoirs, sequence stratigraphy is the main means. As to the favorable reservoirs selected, its evaluation is mainly dependent on well logging. Concerning these aspects, a large number of research have been done, consequently many new methods and techniques have been put forward. However, the demand of further research is still active on these aspects.Aiming at KongNan area of Huanghua depression, elaborate isochronous contrasting framework of stratum was built up, and then ancient geography environment was depicted, the subtle reservoirs was predicted finally.1. The application of high resolution sequence stratigraphyIn 1994, a new school of sequence stratigraphy - high resolution sequence stratigraphy had been set up by T.A.Cross. It bases on the synthesis analysis of core, outcrop, well-logging and seismic reflection section of high resolution. According to the theory of gyre division of datum plane, long-cycle datum plane gyres was divided with reflection interface of seismic, medium-cycle datum plane gyres was divided with well-logging, and short-cycle datum plane gyres was divided with core and outcrop.From the framework, three sequences and eight medium gyres can be recognized in Kong One and Kong Two. Sequence One corresponds to the stratum of Kong Two, Sequence Two corresponds to the stratum from the base of Zao Three of Kong One to the top of Kong Two, and Sequence Three to the stratum from Zao Three to the top of Kong One. Five medium gyre and one half ascending gyre of datum plane can be divided in Kong One. And a half descending gyre, a full gyre and a half ascending gyre of datum plane can be divided in Kong Two.2. The application of wavelet transform to log data Every log curves, recording the evolution of the earth to some extent, can reflect the condition and the influence factor of the forming of sediment strata, such as the change of sea level, ancient environment, ancient geography and ancient climate. Thus the sequence stratigraphy division with logging data will provide useful information for the research of high resolution sequence stratigraphy division.The exact sequence stratigraphy division with logging data depends on the processing method of the logging data. Many methods have been presented so far, such as Analysis of Variance and Analysis of activity function etc. But the methods above achieve the sequence stratigraphy division at certain levels rather than at the gradual levels, which just like the way of manual sequence stratigraphy division. However wavelet transform can extract the time-frequency character from the complex logging data so that the time-frequency of the signal will be localized to detect subtle cycles of the geological process.The log data was processed with 1-D continuous wavelet transform and 1-D discrete wavelet transform to divide the multi-levels gyre periods of stratigraphy. Of all log curves, 1-D continuous dmey wavelet transform of GR log curve can give best sequence stratigraphy division in multi-scales gyre of formation. Of all log curves, 1-D discrete Daubechies wavelet transform of Rt log curve can give best sequence stratigraphy division in multi-scales gyre of formation. Compared to 1-D discrete wavelet transform, 1-D continuous wavelet transform can give better result.The result, processed with wavelet transform, indicates that three sequences and eight medium gyres can be recognized in Kong One and Kong Two, which accords with the result of sequence stratigraphy division.3. The gyre division of linkage-well section in Kongnan areaThe isochronous contrasting framework of stratum and the distribution of sands were obtained with the linkage-well section. Three sequences can be recognized in Kong One and Kong Two. Sequence One is filled with the sands from Canddong fault and Xuxi fault to the inner basin, delta is developed on the edge, and then deep lacustrine facies. Sequence Two is filled with the sands from Xuxi fault to the inner basin, alluvial fan, fluvial and fluvial plain facies is developed. Sequence Three is filled with the sands from Canddong fault and Xuxi fault to the inner basin, alluvial fan, fluvial, fluvial plain and shore-shallow lake facies is developed.4. The log evaluation of the favorable reservoirs with Three Water modelThe favorable reservoirs is processed with Three Water model, the cemention index of free pore, micropore and clay pore is given 1.7, 1.6 and 1.7 respectively. Compared with the production test conclusion, the processing result is favorable. Then isoline plot of sand-bearing ratio and porosity is realized.