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Reservoir Delineation And Reservoir-permeability Units Description Of Deep Volcanic Rock In The Songliao Basin, NE China

Posted on:2012-08-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y X WuFull Text:PDF
GTID:1100330335952047Subject:Mineral prospecting and exploration
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There are a lot of faulted basins in Songliao Basin. Especially,80% of natural gas reserves stored in volcanic reservoirs, which are about 280 billion m3. Therefore, there will be a huge potential for exploration in volcanic gas fields. However, in the actual process of exploration and development, there are a lot of problems such as the rapid change of volcanic reservoir properties, the complex sequence relationship in the volcanic body, the unclear cognition to reservoir formation mechanism and how to reasonably deploy the exploration and development wells. To solve the above problems, this paper carried out some researches.In this paper, the deeper (Yingcheng and Huoshiling formation) volcanic rocks are the main objects of this study, based on outcrops and cores, cuttings, well logs, seismic data of dense well network,using the theories and methods of volcanic geology, oil and gas reservoirs, geophysical and multivariate statistics,we carried out detailed study on lithology,volcanic facies, volcanic edifice and reservoir space. We have emphatically studied the reservoir structure and reservoir-permeability unit in the stratigraphic framework of formation/member-cycle-stage-reservoir permeability unit.1. Geology-geophysical features of deep volcanic rocksDeep volcanic rocks can be divided into four categories and nine sub-categories in Songliao Basin. According to the statistical data of 173 well drillings, the most is rhyolitic which accounts for 32% and the next one is tuff which accounts for 15% . Andesites, tuff lava and basalt account for 14% ,13% and 12% respectively. The least are sedimentary tuff and sedimentary volcanic breccia which account for 2% and 1% respectively. We detailed described the minerals, texture and structure of deep volcanic rocks using outcrop and drilling data in Songliao Basin.We have done some research on conventional logging response of 12 kinds of volcanic rocks which developed different texture and structure in core intervals. The result reveal that basic,intermediate and acid volcanic rocks can be distinguished by GR and density curves, resistivity and three porosity curves have a significantly response to texture, structure and aperture. We summarized 7 kinds of imaging modes using core and thin slice data combined with the FMI image. Tuff structure shows high-resistance and highlight spot mode. The primary stomata shows low-resistance and dark spots mode. Rhyolite structure shows yellow and white and mid-high-resistance and sine curve mode. Breccia structure shows high resistance light block and low resistance dark spots mode. Low angle fracture shows low resistance sine curve mode. Sedimentary volcanic breccia structure shows yellow and orange mid-low resistance sine curve mode. Pyroclastic solution pores show light block containing some dark spot mode. Massive structure shows light block mode.Seismic profiles through cored well have been interpreted based on geological and seismic reflection characteristics. Six kinds of volcanic seismic facies units are identified in the volcanic edifice. Mound-shaped, lens-shaped, dome-shaped are the central facies associations and composed predominantly of explosive, effusive and extrusive facies, respectively. Pond-shaped and wedge-shaped ones belong to the proximal facies associations and composed predominantly of effusive braided lava flow and interbedded explosive pyroclastics and effusive lavas. The sheeted is in the majority of the characteristic distal facies.2. Spatially distributing feature and describe of volcanic reservoirsThis paper establishs a stratigraphic framework of volcanic reservoir which are formation/member-cycle-stage-reservoir-permeability unit, and corresponding volcano eruptive material are volcanic rock body-volcanic edifice-volcanic facies or its combinations-volcanic subfacies or its combinations. Successions of volcanic facies are various in different members and volcanic edifices.The successions of first member of Yingcheng formation are mainly effusive facies→explosive facies. The successions of third member of Yingcheng formation are mainly explosive facies→effusive facies. Successions of facies of pyroclastic edifice are explosive facies→effusive facies→explosive facies. Successions of facies of lava edifice are explosive facies→effusive facies→effusive facies. Successions of facies of compound edifice are explosive facies→effusive facies→explosive facie→effusive facies. There is a successions relationship between subfacies. Successions of the explosive subfacies,from bottom to top,include base surge deposits,interbedding base surge and air-fall,and pyroclastic flow deposits. Successions of the effusive subfacies from bottom to top include lower,middle and upper units.Volcanic edifice have been predicted using angle attribute in dense well network area. Central facies generally distributed in the fault zone and its vicinity. The long axis direction of distal facies is consistent with the fault. Proximal facies is a contiguous distribution. Volcanic edifice of seismic profiles show multiple superimposition. Some facies of volcanic edifice miss bccause of later erosion,for example, distal facies is offen disappeared. Through statistics to long axis, short axis, the thickness and area of volcanic edifice, it is concluded that scale of multi-cone stratified volcano is the most,the next is shield volcano, the smallest is lava dome.Volcanic facies model is established based on stratotype sections and the Y1d1 well and considering the disposition relationship between lithology, facies, edifice and fault and joint.This models reveal that explosive facies were developed in the early volcanic eruption cycles. Lateral-extension and vertical-thickness of the explosive facies is some thousand and several hundred meters respectively. They are wedge-shaped with a steeper upper slope and gentler lower slope showing an average slope angle of 15°. Effusive facies generally occured in the middle of an eruption cycle and covered on top of the explosive facies. They can extend up to some thousand meters and get a thickness up to several hundred meters. They are lenticular-shaped and pinch out laterally,with a gentler upper slope and steeper lower slope showing an average slope angle of 20°. Extrusive facies generally occured at the end of an eruption cycle. They often cut through and cover other lithofacies. Their stretches and thickness are usually no more than 1km. They are mushroom-shaped with a large flat roof and sharp border.3. Formation of reservoir space and analysis of reservoir performanceWe make surface pores statistics to 167 representative samples including 16 types lithology and 12 kinds subfacies which come from outcrop and drilling area in Yingcheng Formation. The results show that:①The ratios among the primary pores and secondary pores and fracture of vesicular lava, dense lavas, pyroclastic lavas, pyroclastic rocks and sedimentary pyroclastic rocks are respectively (7.6:1:1.4), (1.8:1:2), (2.7:1:1.8), (0.4:1:0.6) and (0.3:1:1.1).②Volcanic conduit dominanted by inter-breccia pores and fissures, from the bottom to the top of explosive facies and effusive facies,the proportion of primary pores rise and the proportion of secondary pores and tectoclase drop, condensed shrinkage fissure had been identified mainly extrusive facies. Volcanic sedimentary facies are mainly secondary pores and secondary fissures.③The distribution of primary pores in different volcanic rocks change largely and the next is secondary fracture, besides, the primary microporous, secondary pores and the primary cracks change not so obviously.Discussed the relationship between reservoir space and pore-throat structure, porosity and the permeability of 15 kinds lithology, conclusion that the pore-throat structure can be classified into 5 types:coarse throat type, mid-coarse throat type, partial coarse throat type, minute throat type and fine throat type. Lithology developed excellent pore-throat structure are stomatal rhyolite, rhyotaxitic rhyolite, Spherules rhyolite,ignimbrite,brecciated lava,hydrothermal breccia and breccia. The porosity can be sorted into 6 kinds:single peak and high pore type, twin peaks and high pore type, medium pore type, mid-low pore type, partial low pore type and low pore type. Similarly, lithology with good porosity is stomatal rhyolite, rhyotaxitic rhyolite, breccia, brecciated lava, ignimbrite, and brecciated lava. In addition, there are also 5 types of permeability; they are high permeability type, mid-high permeability type, medium permeability type, mid-low permeability type and low permeability type. And the stomatal rhyolite,massive rhyolite, massive adnsite, vesicular and amygdaloidal basalt, rhyotaxitic rhyolite, breccia lava and breccia have good permeability. Comparing the results above, we can draw a conclusion that the stomatal rhyolite, rhyotaxitic rhyolite, spherules rhyolite, ignimbrite, breccia lava and volcanic breccia are easy to form good reservoir, and massive rhyolite, massive basalt and sedimentary tuff have relatively low reservoir capabilities.4. The study of volcanic reservoir-permeability unitsPhysical property barrier and volcanic/sedimentary rock barrier can be recognized in reservoir-permeability units. Generally,the features of the former are the upper limit porosity and permeability is respectively 3% and 0.01×10-3μm2,and the lower limit of density is 2.57g.cm-3. The features of the latter are the upper limit porosity and permeability is respectively 3.9% and 0.01×10-3μm2,and the lower limit of density is 2.55g.cm-3.They can be identified by logging. Physical property barrier is micro-tooth box form, resistivity curve and density curve are high amplitude, interval transit time curve and neutron curve are low amplitude. The curves of volcanic/sedimentary rock barrier are serrate.The concept of reservoir-permeability units is that belongs to the same stage volcanic rock body, it may be subfacies or subfacies association that have relative vertical and horizontal porosity, permeability and number of pore-fracture. Physical properties of rock can be gradually variational but not homogeneous in a single reservoir-permeability units. In essence, volcanic reservoir-permeability units are also pore-fracture units. The relationship of reservoir space and seepage channels can be divided into nine groups,including hole-type, macroporous and microporous type, pore and fissure type, macrofissure and pore type, mesofissure and microporous type, macrofissure type, microfissure and microporous type, macrofissure type, macrofissure and microfissure type, hydrothermal fissure type.Reservoir-permeability units of outcrop and cores can be identified combining description of pore-fracture with physical property. The first step of distinguishing between reservoir-permeability units is to identify isolated barrier beds in uncored wells, the next is to divide reservoir-permeability units. Classification of reservoir-permeability units are based on cluster analysis of porosity, permeability, density, interval transit time and neutron of cores,and then establish a discriminant to identify uncored intervals.Types of reservoir-permeability units are controlled by lithology, facies and tectonic. Good lithology and facies of reservoir tends to be excellent reservoir-permeability units. This analysis of dense well network area reveal that ignimbrite, tuff lava, volcanic breccia lava of pyroclastic deposits of explosive are excellent reservoir-permeability units. Stomata and rhyotaxitic rhyolite middle and up of effusive facies are good reservoir-permeability units. Profile of reservoir-permeability units indicating that high position are apt to form excellent ones.5.Diagenesis evolution and controlling factors of pore-fracture of volcanic reservoirsPrimary pore-fracture are related with texture and structure of volcanic rocks (including vesicular structure, lithophytic structure, vesicular and amygdaloidal structure, rhyotaxitic structure, perlitic structure, columnar joint, intergranular texture,melting corrosion). Tectonism,weathering,dissolution,devitrification are conducive to the formation of secondary pore-fracture.Based on formation stage and variation tendency of pore-fracture,volcanic rock diagenesis stages are divided into syndiagenetic stage, epidiagenetic stage, early/ moderate/late buried diagenetic stage. Primary pore-fractures formed in syndiagenetic stage, they were filled or cemented solution pore in the later. Surface porosity of primary pore-fracture declined form 25% to 7% . Secondary pore-fracture were mainly developed in syndiagenetic stage and moderate buried diagenetic stage, and the increased quantity of pore-fracture was 5% . The destruction of pore-fracture occurred on the early and late buried diagenetic stage. Surface porosity of secondary pore-fracture declined to 1.8% at last. The quantity of collective pores of vesicular lavas changed along with secondary pore-fracture,declined from 25% to 10%, but they are still composed of primary pore-fracture. We establish well-logging response of diagenesis using cores data. The division of diagenesis and types of pore-fracture are based on cuttings and logging,profile distribution of pore-fracture is achieved by multiple drilling.
Keywords/Search Tags:Songliao Basin, Volcanic Reservoir, Volcanic Facies Models, Volcanic Reservoir-permeability Units, Formation of Reservoir Space, Diagenesis, Reservoir Control Factors
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