The Prediction Of Qum Formation Fracture In Kashan Area, Iran

The central of Middle Iran Basin locates in the north of Kum, with120,000km²,while the area of Kashan is4958km², where has complicated surface andunderground situation and it is highly risky to explore. The Sinopec finished Arn-1well in2004, which found industrial oil flow in Qum formation, but later theexploration of wells Fkh-1, Arn-2and Arn-3failed. The exploration results showedthat the gypsum rock on the bottom was the cap rock of Alborz oil field and Sarajehcondensate oil field, and marlite of Qum E section was the reservoir. The gypsumrock of Qum D section was the cap rock of Aran oil-bearing structure, while thelimestone and marlite of Qum C₄section were the reservoir layers. C₄section isfracture reservoir and has low matrix porosity. Fracture, which are controlled by foldand faulting and effected by thickness and lithology of hard-line level, are seepagechannels and also are important reservoir space.This paper, based on the foreign and domestic researches, combined surface withunderground and geological with geophysical, to devolp the research method ofstructure of Qum, description of fracture of surface outcrop and core, analysis of drillwell, seismic ea.al. Analyzes on the characteristics of Qum fracture and the maindevelopment zone from the morphology （length, size, distribution and lithologyrelation, etc.） and the relation of constructure.The specific method is to do researches on the fissuring and joint appearing inNavab surface anticline in Kashan area and to analyze how structure controls Qum ingeology. The studies on core with joint and cleavage and with logging imaging showthe basic characteristics of joint and cleavage, and conformation of fracture. The3Dseismic data of Kashan area underground are used to identify the faults in the verticaland flat conformation, distribution and developmental characteristics. Finally, theintegrated coherent analysis and the curvature method are applied to processing the3D seismic data to study the fracture surface development characteristics and primary controlling factors.Comprehensive analysis shows that Qum fracture porosity value is small, themaximum porosity is not more than2.86%; but the fault zone near the fractureporosity is high, generally greater than5%, up to13%. It indicates that the fractureporosity significantly is affected by the fault effects. But this narrow fracture ribbon isgenerally not more than10m wide; fracture porosity development is generally nearthe fault zone, and formed by folding the role of fracture porosity is much smaller, notmore than2.86%. The middle Porosity develops area located anticline axis in theregion, particularly by its reverse fault and back thrust reverse fault posed by "V"word tectonic zone, on the one hand affected by fault, on the other hand controlled byfolding. So the porosity is bigger, but the width is narrow, generally only100m.Therefore fracture is mainly affected by folding, few by faulting, partly by both,where is the main exploration zone.The developed fracture system C₄sub-section and small fractures of Arn-1wellare up to50%, where30%of the micro, small fractures connect well. Most fracturemorphology is high angle joints, followed horizontal joints and low angle joints.Arn-1well, in which sub-paragraph3538.m-3569.0m C₄fracture is well developed, isthe high quality reservoir. Fracture morphology dominated by high angle joints;maximum fracture width reached367.1μm, averages out to166.5μm; fractureporosity averaged0.012%, indicating that the fracture essentially connected joint;fracture permeability with high value, the average reached1121.6md; Arn-2Well C₄sub-paragraph3288.m-3367.0m is micro-fractures, small fracture s is only about5%,95%of the micro-fractures is the isolated joint, not connected to each other, only5%of the micro-fractures is connected seam. Overall, the reservoir of the fracture is notwell developed; Fkh-1Well C₄sub-paragraph is not development of the fracturesystem, fracture almost full filled, very small part is the half-filled, filledmicro-fractures only, no connecting from each other. The fracture morphology ismainly the low-angle fracture;The coherence analysis based on seismic data and principal curvature for IranKashan region TM1-TQb layer predicts fracture zones can be drawn in the study areaundulating structure, faults, and the Aran anticline in the north TQ-TQb layerdevelopment, the anticline structure gradually disappears under Qum. Coherence timeslice shows Qum under the top of the depth of200-300ms there is a fracture zone,coherence analysis on the main role of cap rock of TQd salt layers shows that degreeof fracture development is high, the main development area is the western part of No. 1and the connection of eastern part of No.4and junction of No.6and7. Mainpurpose of structural transition layer TQu fracture with the fracture, the mostfavorable for the fracture zone, tectonic uplift of parts of the Qum relatively low levelof fracture development, Arn-2well may be in parts of tectonic faults zoneconversion and Arn-3in the fracture development between Arn-1well. In addition,the principal curvature also shows that fault south eastern end of the2nd developmentof a certain size small faults, suggesting a favorable time for the fracture zone; Arn-1well anticline at the top, Arn-3well and the area at the top of anticline fracturestrength for the greater southeast region, based on curvature analysis, the twoturn-side anticline （anticline shoulder）, North West, the most to the development ofvertical tensile fractures; Second, in the long axis of the high points, plunging end ofWest, is also well developed near the fault, but anticline wings are non-development.Therefore, both the fracture development levels, one is in tectonic transitionribbon, and the other is in tectonic high part, are low. Comprehensive analysisindicates that the position of well Am-1show better fracture development than wellArn-2. Well Arn-1connects the fracture system to oil generating depress, but probablywell Arn-2locates at fracture development zone of the tectonic transition section.