| Since the establishment of the “Tight sandstone gas reservoir” concept in the1970s, significant research and development have been conducted worldwide on thedefinition, characterization, formation, methodology, technology, and producingprocess. In China, a number of tight sandstone gas reservoirs have been discovered,such as the Sulige gas field of the Ordos basin, and the Xujiahe formation in themiddle of the Sichuan basin. Both the incremental proven reserve and the productionare rapidly growing every year. However, little research has been done on deep tightsandstone gas reservoir in the Changling fault depression.This dissertation is focused on the research for deep tight sandstone gas reservoirsin the Denglouku formation and the1st member of Quantou formation in theChangling fault depression. This work takes into consideration the reservoircharacteristics of braided fluvial deposition, including low porosity, low permeability,large buried depth, and dramatic lithology horizontal changes. This work synthesizesdata from drilling, logging, core samples, laboratory analysis, gas test results, andseismic data, among others. This work includes research on sequence stratigraphy,seismic facies, sedimentary microfacies, log interpretation, diagenesis, effectivereservoir distribution and reservoir master factors analysis. It is based on well-seismiccombination. It combines geology, seismic, and well logging studies. It appliesvarious new technologies in geophysics, and synthesizes various information(including seismic reflection configuration, seismic attribute extraction, seismicinversion, hydrocarbon detection, etc.). This research reveals the relationshipsbetween various seismic information and reservoirs. Reservoir distribution is furtherinvestigated. Relatively high-yielding rich regions are predicted. The drillingtargets of Dalaoyefu are prioritized through a comparative study of representative gasreservoirs between the Fulongquan and the Shuangtuozi areas.Through the integrated interpretation of the seismic and geology data for16regional sections, totaling2121.74kilometers, in the Changling fault depression, the geological stratification is conducted, for the first time, for the Denglouku formation(from1st to4th), and the1st member of Quantou formation in the area. Thesequence boundary characteristics in terms of seismic and logging responses areclarified. The sedimentation boundary for every layer is determined. The angularunconformity between the Denglouku formation and the Yingcheng formation is found.The interface between the Denglouku formation and the1st member of Quantouformation is determined to be the sedimentation conversion surface. Theidentification and classification of medium-term base level cycle of the Dengloukuformation and the1st member of Quantou formation is conducted with the aid oflogging, well logging and seismic data. The Denglouku formation is divided into4segments.High resolution seismic sequence interpretation reveals clear characteristics ofstacking patterns for short and medium term base level cycles within the Dengloukuformation and the1st member of Quantou formation. Bi-directional super and onlapare normally seen above the bottom interface during the rising period of the mediumterm base level cycle. Internal short term cycle presents retrograding and stackingpatterns. During the falling period of the medium term base level cycle, toplaps areusually seen near the top interface. Internal short term cycle presents stackingpatterns. Lateral continuity is poor for the short term cycle. Transitional continuityis good between the base level rising and falling. Based on the comparison of themedium term cycles, the stratigraphic framework of the high resolution seismicsequence and drilling sequence is established for the region. Thepalaeogeomorphological characteristics for every period become obvious.In this research, the drilling and seismic analyses are major considerations, alongwith shale color, core description, sandstone thickness, and sand-to-shale ratio. Majorsedimentation types are identified for the Denglouku formation and The1st member ofQuantou formation. Those sedimentation types include alluvial fan, fan delta, braidedriver-braided river delta, meandering river-meandering river delta, and lacustrine.Sedimentary facies plans for every period are developed. The following sedimentation evolution features are clarified for the Denglouku formation and The1stmember of Quantou formation:（1）For the1st member of Denglouku formation: Several tectonic zones aredistinguished along the west-east direction. Within every tectonic zone, multipleregions along the east-west direction can be further defined due to differentcharacteristics.（2）For the2nd member of Denglouku formation: The southern and northernrift zones are enlarged. The eastern and western regions of the depositional area inthe north become connected. The braided river delta sedimentation system is themajor development.（3）For the3rd member of Denglouku formation: The lake basindepositional area continues to grow. The separate regions in the north and southmerge and form one large Changling rift zone. Due to the severability of theLacustrine deposits, two lake regions are formed, one in the east, the other in the west.An alluvial fan is developed in the southeastern slope. A fan delta is developed at theGu-1fault downthrown. Braided river delta deposits are developed in other regions.（4）For the4th member of Denglouku formation: The same characteristicsof the deposition and the distribution of the Segment3continue into the Segment4.The diagenetic facies study shows that the reservoirs of the Denglouku formationand the1st member of Quantou formation are mainly at the A2diagenetic times.Affected by dissolution, two secondary pore zones occur at2000-2500m and3500-3800m.Interpretation models for the reservoir parameters, gas reservoir identificationmethods and standards are established for the Denglouku formation and the1stmember of Quantou formation, through the relationship study of the “four-properties”(lithological, physical, electrical and petroliferous properties). Log interpretation isconducted for more than60wells. This work reinforces the basis for the studies forthis area. Refined stratum comparison and classification are conducted for the Dengloukuformation and the1st member of Quantou formation in the Dalaoyefu area, byseismic-geology comprehensive studies.9sub-stratums are classified.Development properties for every sub-stratum is determined. Interpretationmethodology for the seismic facies of braided channel sands in the Dalaoyefu area isestablished. Seismic facies models of6sub-classes of sands are recognized, whichbelong to two categories: river erosion and lenticles. Fully3-D seismic interpretationis conducted for every sub-stratum. Development and distribution properties of thesandstones are determined.Analysis of the typical gas reservoirs in the Fulonquan and Suangtuozi areas,along with comprehensive study of the drilling, gas test, seismic interpretation andreservoir prediction in the Dalaoyefu area, reveals the natural gas accumulationcharacteristics for this region. In summary, transport conditions, tectonic settings andphysical properties of reservoirs are major reasons for the gas accumulation.Locations for4wells are proposed after thorough analysis of gas resource potentialsand exploration status in the Dalaoyefu area. This work is expected to open up newopportunities for further exploration of this area. |
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