Diagenesis Of Fuyu Oil-bearing Reservoir In The North Of Qijia Region And Its Effects On The Development Of Reservoir

The north of Qijia region is in the Dorbod Mongolzu Autonomous Counties which locate in the Daqing City of Heilongjiang Province, whose east is Daqing Placanticline, the west is Qijia oil field, the south is Lamadian Town, the north is Zhangqi Country Lindian Town, it is in the north of Qijia-Gulong Sag Central Depression region which is in the north of Songliao Basin. In the evolution of Songliao Basin Qijia-Gulong Sag undergo four stages: fault depression-fault and depression-depression- uplifting.Through the observation and description to core, the major sedimentary facies are delta plain and front subfacies, the oil shows are obvious. Rock types are mudstone with silt, fine-sandstone, middling-granularity-sand, major clastic particles components are quartz, feldspar and lava debris, the contents of feldspar and lava debris are similar. The cement type is carbonate with iron and magnesium, siliceous cement, clay cement and zeolite. The matrixes include mud and argillaceous. The content of fillings of sandstone is 9%～17%.The major diagenetic evolution of quartz is overgrowth which is the result of chemic deposition in acidity liquid environment; in addition the corrosion of quartz shows that the pH value augment is along with the increasing of temperature in diagenetic evolution. The diagenetic evolution of feldspar is overgrowth which occurred in high diagenetic temperature and alkalescence solution; on the side the clayization of feldspar represents that the illite and illite hydromica are on the surface of feldspar; the degree of the corrosion had the direct relationship with the physical character of reservoir. Lava debris is the important fragment component in this region, the major is acidic and intermediate, the minor is basic; the dissolved pores in debris granule is an important pore type. Beside secondary enlarged quartz and feldspar, carbonate cement and clay mineral are the most chemic deposition cement in amount, zeolite cement is less but it is also the important indicate of the diagenetic phase.The depth of Quan-4 member is in the range of 1800～2300m in this block, the depth diversification is small, so the dagenesis didn't have great differences. The idiographic dagenesis types are: compaction, cementation and the corrosion, dissolution of component. The compaction is the major dagensis type at the top of Quan-4 member.Carbonate cements are calcite or calcite with iron and magnesium; the cementation is not strong at some positions, the proportion of the fillings is small, the cementation is strong at other positions, the calcites show intergrowth structure; the origin of Ca²⁺ is the albitization of potassium feldspar, the increasing of temperature, the reducing of partial pressure of CO2 is propitious to the sedimentation of carbonate.Fe²⁺,Mg²⁺ come from the translation of montmorillonite to illite, mafic-intermediate volcanic debris'dissolution also could increase the content of Fe²⁺,Mg²⁺. The major representation of silicic cementation is secondary enlarging of quartz, the major quartz particles are 3～5 stage, silicic cement came from the of alteration volcanic glass, the transformation of clay mineral, the dissolution of feldspar, pressure solution.The clay minerals in this block grew on the surface of apatite like pellicle, the degree of clayization rose with the increasing of depth, the diversification of illite's content with the increasing of depth is not obvious, the degree of crystallinity had the ameliorative trend, judging from the result of anlysis, the kaolinite just appears a higher belt at the bottom of Quan-4 member; illite smectite mixed layer content shows negative correlation with illite content; chlorite distribute in the northwest area which is close to provenance, it could be translate from kaolinite, if the interlayer water contained Fe²⁺,Mg²⁺ it could translate from illite or potash feldspar.The zeolite is the important attribute of diagensis in this block, whose formative temperature is 120℃. Dissolutions include the dissolution of calcite with iron and magnesian, denudation and metasomatism include the calcite'measomatism to quartz and the albitization of potash feldspar, the former is result of increasing of pH value and temperature and the depress of CO2 content; the latter is the result of replacement of Na+ to K+ in the potash feldspar whose exhibition is the decrease of potash feldspars and the manifold of albite.Through the thermometry on fluid inclusions we got the conclusion that the temperature ubterval of diagenesis is 70～135℃in Fuyu reservoir the north of Qijia region. According as the fresh water–brackish aqueous medium claslite diagenetic stage plot sttribute in the petroleum industry standard ( SY/T5477-2003) clasolite diagenetic stage plot, combining with practical situation of diagenesis in this block, we divide the diagenesis of Quan-4 member into three phases: the metaphase diagensis phase ( MDP) Aâ… , Aâ…¡and B, approximately the demarcation temperature of MDP-A and MDP-B is 120℃. The MDP- Aâ… only distributes in the Fâ… 1 and Fâ… 2 little layers. The MDP- Aâ…¡distributes in very little layers in most area which decreases to northwest with the increasing of depth, MDP-B distribute at southeast whose area increases to northwest with the increasing of depth, the changing law above are anastomotic with the characters of construct and provenance in the north of Qijia region.Through the integrative analysis including the observation under the microscope, we compartmentalize four diagenesis styles: silicic cementation facies, calcitic cementation facies, clay loop facies and admixture facies; combining with diagenesis phase distribution and precipitation facies distribution, we make the distribution of the diagenesis facies of seven little layers, and than draw the pictures for the research of reservoir's ventages.Combining with the result of ventage parametric statistics in different diagenesis phases and diagenetic facies, we get the conclusion: the influence of diagenesis to pores and secondary pores is not quite obvious, MDP- Aâ…¡is a little better than other two phases, the four diagenetic facies types we divided through the characters under the microscope: silicic cementation facies, calcitic cementation facies, clay loop facies and admixture facies, the degrees of their ventage upgrowth become worse in turn. The diagenetic research provides theoretic and realistic gist for the study on secondary pores zone.