Shale gas exploration and development in Sichuan Basin had achieved a major breakthrough.But business development focused only on marine shale gas in shallow layers (vertical depth<3 500m) of Wufeng Formation-Longmaxi Formation.Therefore，business development of deep shale gas (vertical depth >3 500m) in Wufeng Formation-Longmaxi Formation is the key to the rapid growth of shale gas production in the Sichuan Basin.In the literature，authors analyzed the geological characteristics of deep shale gas of Wufeng Formation-Longmaxi Formation in southern Sichuan Basin through particular dissection and analysis of deep wells，comparing with the shallow layers.The thickness of organic-rich shale in deep region of southern Sichuan Basin is more than 120m，which is larger than that of shallow layers in Fuling.The vertical TOC change is the same，and the thickness of high quality shale is about 40m in the two regions，but RO is higher in the deep region of southern Sichuan Basin.The calcareous content of the organic shale increases，and the silicon content decreases from Fuling gas field to the deep region in southern Sichuan Basin.Research shows that the shales in Wufeng Formation-Longmaxi Formation of the southern Sichuan Basin from deep to shallow layers do not have so much differences in depositional environment，lithology，TOC，etc.There are four major differences：the porosity of shale in deep region of Southern Sichuan Basin is higher than that in Fulin because of denudation pore.The gas-bearing properties is better in deep region of southern Sichuan Basin with better preservation condition than that of shallow region in the Fuling gas field，but the gas-bearing property is worse in the local region with stronger structure deformation and the basin boundary fault zone.The shale gas resource in the deep region of southern Sichuan Basin is great and has wide prospects for exploration and development.In order to make breakthrough in deep shale gas commercial development as soon as possible，the authors propose the follow works as：Strengthening evaluation of small layer contrasting，fine structure explanation，fracture prediction；strengthening research of drilling and fracturing technology for deep shale gas；strengthening research of the wells column and supporting technology for efficient production of shale gas.
Chemometrics has unique advantages in comprehensive consideration of the influence of multiple parameters and division of the species category of samples or variables，especially for data mining of large data sets and regional oil-oil and oil-source correlation.This paper introduces in detail two commonly used chemometric oil-oil and oil-source correlation methods，hierarchical cluster analysis (HCA) and principal component analysis (PCA) as well as the newly introduced research method-multidimensional scaling (MDS)，and a detailed comparison and discussion of the principles and scope of these methods.In terms of application chemometric methods to geochemical correlation，we need to be cautious about sample screening，the choice of correlation parameters，data preprocessing，and the selection of high-dimensional spatial distances between samples，because this is directly related to the reliability of the correlation results.
The Penglaizhen Formation 3rd member (Peng 3 member for short) gas field has good development potential in the Upper Jurassic in Shifang area in western Sichuan Basin.Based on detailed observation from well cores，ordinary and mold thin section，porosity，permeability，mercury experiment analysis results of some samples，combined with reservoir log interpretation and seismic prediction，well seismic integration，sequence，sedimentary facies，reservoir characteristics，reservoir distribution prediction and comprehensive evaluation of Peng 2 gas-pool and main object strata 3 sandstone groups ( JP32 ) are researched in this area from Western Sichuan Depression area，and the controlling factors of effective reservoir development are analyzed.The research results show that Peng 3 member can be divided into five sand groups.The internal sandstone groups strata thickness is relatively stable，which shows that the strata were deposited in sedimentary environment of stable structure，flat lacustrine basin.Combined with the characteristics of litho-facies marks，facies sequence character analysis，logging response and seismic facies，the shallow-water river-controlling gentle blanket delta front underwater distributary channel is the most favorable sedimentary micro-facies.In JP32 sandstone groups，the pore type of fine debris sandstone reservoir rocks mainly has the characteristics of low porosity，low to extra-low (or near tight) permeability.The plane distribution of sand bodies in JP32 sand group is controlled by river boundary.Compared with distributary channel sand bodies，the distribution range of effective reservoirs，especially，the high-quality effective reservoirs of JP32 sandstone groups are relatively limited with the discontinuous band characteristics，and are mainly located in the northern and middle channel.Comprehensive analysis shows that the key of the development of high-quality and effective reservoirs is controlled by lithologic distribution of favorable sedimentary micro-facies，and to a certain extent controlled by relatively high tectonic sites，fractures and fractures.
It is the key point to find the sweet point in the process of exploration.Based on the experimental analyses on particle size，X-ray diffraction，casting thin sections and mercury injection，combined with imaging logging，we performed a series of research on tight sand petro-physical characteristics，and concluded the main controlling factors of high quality reservoirs in Linxing area，Ordos Basin.The reservoir pore throat size consists of fine-small pore throat，intergranular dissolved pore and dissolution particles are the main reservoir space，and porosity and permeability mainly concentrates in 4%-10% and (0.1-1)×10-3μm2，respectively，belonging to low porosity，low permeability reservoir.High quality reservoir surface is controlled by sedimentary micro-facies and micro-cracks，and is also influenced by diagenesis in the longitudinal direction.Dissolution is also one key factor to improve the reservoir property.As facies variation，corresponding physical property also changes.The sand flat of tidal flat，distributary channel of delta facies and edge beach of meandering river facies are of best quality.Good reservoir can be formed by the development of pore of the coarse-grained sandstone.The site micro-fractures derived from tectonic movement and Zijinshan magma intrusion and cooling may be the site where high quality reservoir develops.The secondary pores and dissolution development which are formed by the dissolution of feldspar in the diagenetic process are the basis for the development of the quality reservoir of tight sandstone.Part of mineral and rock composition have dual influence on reservoir property: diagenesis exacerbated the densification of the reservoir at the same time，and the amount of brittle mineral，authigenic clay minerals and carbonate rocks，pyroclastic construction play an important role in the formation of high quality reservoirs.
The deep fractured tight sandstone gas reservoir of K1bs in Keshen block of Kuqa Depression has a high temperature and high pressure system and very complex gas-water distribution characteristics which takes a great challenge for exploration and production. This article carried out a research on the genetic mechanism and model of gas-water distribution in these gas reservoirs through systematical analyses of reservoir characteristics，source-reservoir relationship and gas-water distribution of tight sandstone gas reservoir combined with relative permeability test. Research shows that the tight sandstone reservoir in K1bs has strong reservoir heterogeneity which is demonstrated by matrix with complex pore structure whose pore space gives first place to residual intergranular pore and intergranular dissolution enlarged pore and different scales of fracture network system formed with faults and fractures；Keshen block is distinguished from other domestic and abroad tight sandstone gas reservoirs with adjacent source-reservoir type by remarkable separation of source and reservoir that makes gas a long secondary migration to tight reservoir through faults and fracture system；Gas charging level is in control of fault-facture system，fracture density，matrix physical property and pore structure so that the closer to fracture，the greater reservoir gas charging level will be；Under the effect of gypsum-salt cap rocks，gas reservoir water is reverse discharged mainly through faults and fracture network and replacement effect is the main reservoir-forming mechanism for gas；and then the gas-water distribution pattern of the deep fractured tight sandstone gas reservoirs in Keshen block was classified into three types，i.e.，normal gas-water distribution pattern with fracture network developed，gas-water distribution pattern with fracture network non-developed and gas-water coexistence distribution with fracture network partly developed.
Based on the results of conventional geochemical analysis，zoogloea fossils were discovered in the low mature marine hydrocarbon source rocks and coal seams in south China，and the sizes of bacterial-like fossils ranged from dozens of nanometers to several microns with circular，oval，oblate shapes，which were observed in the thin section and scanning electron microscope.The confirmed bacterial-like fossils in the Permian source rocks were mainly formed by the symbiotic sulphur bacteria with gypsum.Abundant nanoscale bacterial-like fossils discovered in the Chengkou section within Cambrian strata were mainly in the shape of rod-short columnar.Many possible bacterial-like fossils were found in Permian，Silurian，and Cambrian source rocks with high maturity under the scanning electron microscope.There was still some preliminary perspective as follows: bacterial-like fossils were prevalent in the source rocks and had a symbiotic relationship with source rocks，especially in the mudstone，siliceous rocks，some stratum containing coal seam and gypsum；the bacteria on the surface of mudstone formed microbial mats；the bacteria in siliceous rocks had the behavior of dissolving silicon；the symbiotic bacteria with gypsum in the coal seam were sulphur bacteria playing important role in the formation of gypsum.The study of the formation mechanism and environment of bacterial-like fossils via online analysis on microdomains will provide new insights for evaluation of source rocks.
The Upper Paleozoic coal-bearing strata in Yuzhou region at southern North China Basin have good exploration potential for unconventional hydrocarbon reservoirs，therefore systematic evaluation of potential source rocks is indispensable.This study selected full core hole ZK0606 which perfectly revealed Upper Paleozoic，systematically collected samples of coal rocks，mudstones and carbonate rocks of Upper Paleozoic，and analyzed the samples to obtain the parameters of TOC，hydrocarbon generation potential，chloroform bitumen “A”，organic maceral，vitrinite reflectance and kerogen carbon isotopes.Test results show that coal rocks，mudstones and carbonate rocks are all possibly potential source rocks in the Upper Paleozoic.Vertically the source rocks are continuous in Taiyuan Formation and the lower part of Shanxi Formation，mainly distribute in the nearby coal bed with small thickness in the upper part of Shanxi Formation and Xiashihezi Formation，seldomly in the Shangshihezi Formation.The vertical distributional regularity of source rocks is mainly related to Late Paleozoic transgression.The kerogen type of coal rocks and mudstones are type Ⅲ，but the carbonate rocks are also mainly type Ⅲ，apparently different from the general carbonate rocks，this abnormal phenomenon mainly attributes to the special sedimentary environment of the carbonate rocks.The thermal evolution degree of Upper Paleozoic source rocks of ZK0606 has reached mature-highly mature stage，and RO increased gradually by depth.The higher degree of thermal evolution may relate to the higher paleogeothermal gradient in this area.According to the essential characteristics of source rocks and the evaluation methods of coal-bed methane and shale gas，the Ⅱ1 coal layer and its upper and lower mudstone of Shanxi Formation are the main target layers of coal-bed methane and shale gas exploration，and the southeast part of Baisha syncline is a key exploration area.
In order to establish the reverse fault evolution model in clastic strata，on the basis of systematic observation and experimental analysis of the fault on the western margin of Qaidam Basin，combined with the research of the evolution of fault from both macroscopic and microscopic aspects，the internal structure and lateral sealing ability of different scale fault zones were analyzed.The results show that the evolution of fault zone has three stages：(1) When fault throw is minor，the fault is the “one factor” structure，it consists of damage zone and slipping surface；(2) When fault throw is moderate，the fault is the “two-factor” structure，it consists of damage zone and fault core，the fault core is filled with fault gouge and fault breccia；(3) When fault throw is large，the fault core is filled with fault gouge only.When a certain fault throw is reached，the fault begins to have certain sealing ability，the larger the fault scale (throw)，the greater the content of the fault gouge，the higher SGR，the greater the lateral sealing ability of the fault.
The Upper Triassic Babaoshan Formation in the Babaoshan Basin is a set of terrestrial sedimentary rocks dominated by volcanics and clasolite.Multiple layers of source rocks with various thickness are developed in these sediments.Through the route geological survey，drilling and sampling testing system，this paper analyzes the abundance，type and maturity of organic matter of the source rocks of the Upper Permian Babaoshan Formation in the Babaoshan Basin.The results show that the average value of organic carbon content (TOC)of the dark shale is 2.23%，indicative of good source rock.The organic matter belongs to (humus)type Ⅲ kerogen.The thermal maturity (RO)is 2.53%，and it is at highly mature stage.The sedimentary environment is a fluvial lacustrine depositional system.Therefore，it is considered that the shale gas reservoirs have a good prospect in the Upper Triassic Babaoshan Formation.
Shale oil exploration made great progress in the second member of Kongdian Formation in Cangdong Sag and several wells got industrial oil flow in the shale segment which was considered as hydrocarbon source rocks.However，the internal lithologic and organic geochemical features have not been studied in-depth.Based on the analysis of conventional thin section，whole rock X-ray diffraction，organic carbon，vitrinite reflectance，soluble organic components of rocks，saturated hydrocarbon chromatography and saturated hydrocarbon mass spectrometry，the lithology and organic geochemistry characteristics of the fine grained lithologic of the second member of Kongdian Formation in Cangdong Sag were systematically evaluated.The evaluation results of the second member of Kongdian Formation shows demonstrate complex rock mineral composition，high abundance of organic matter with Type Ⅱ1 and Type Ⅱ2 kerogen，and low-medium thermal maturity.Normal alkane extract from source rock contains single peak type and double peak type；source rock has phytane advantage and only few samples have low content of gammacerane，indicating strong reducing environments；C29sterane content is obviously higher than C27or C28 sterane，C27 sterane also has relatively strong peaks.The organic matter of the second member of Kongdian Formation in Cangdong Sag is mainly from the higher plant，and also has lower aquatic organisms and algaes.
Formation water is an important fluid coexisting with oil and gas in petroliferous basins，its chemical characteristics are of great significance to the evaluation of oil and gas preservation conditions.Reliable Pinghu-Huagang Formations water data suggest that: The total dissolved solid (TDS) is low，with average of 21657.37mg/L.Na++K+，Cl-，HCO-3are dominant ions and water type is mainly NaHCO3 type，r(Na+)/r(Cl-)，r(SO2-4)×100/r(Cl-)，and r(Mg2+)/r(Ca2+) are high，and r(Cl--Na+)/r(Mg2+) is low.These characteristics reflect weak concentration and deterioration of formation water and it is in half open-half close regional hydrodynamic slow alternation zone.Except the evaporation and concentration of freshwater-brackish water of lake basin，the source of formation water also has salinization that seawater along the open structure infiltrates into synsedimentary water of underlying strata.Halite dissolution is mainly origin of Na+ and Cl-，kaolinization of albite makes important contribution to HCO3- formation.There are close relations between chemical compositions of the formation water and natural gas reservoirs.While the formation water is of low TDS(<25 000mg/L)，NaHCO3 water type，low r(SO2-4)×100/r(Cl-) (<8)，low r(Mg2+)/r(Ca2+) (<1.5) and r(Na+)/r(Cl- ) is at 1-1.6，r(Cl--Na+)/r(Mg2+) is from -80 to -0.5，there may be beneficial to preserve natural gas.
Perforation is important to fracture initiation and propagation in horizontal wells.This study puts forward an in-plane perforation methodology to decrease the breakdown pressure and improve the fracture-wellbore connection，and large-scale polyaxial tests are deployed to confirm the idea.The breakdown pressure of the tests is compared to those of four models，and also the fracture geometry is observed and analysed.The tests show that the in-plane perforation which means perforation holes and tunnels in the same plane and perpendicular to the minimum horizontal stress reduces the breakdown pressure effectively，and also reduces the near wellbore tortuosity and improves the fracture-wellbore connection.These observation and findings could be used to optimize the perforation and fracturing jobs on site.
In order to improve the post-compression effect of tight sandstone gas reservoirs，taking Shaxi Temple Formation JS12 gas reservoir in the ZH structure of Western Sichuan Depression as an example，the microstructure of the reservoir is studied by means of electron microscopy and constant speed mercury pressure testing，and the sensitivity of the reservoir and the damage of water lock are evaluated.The gas reservoir has the advantages of easy expansion and migration，because of high content of clay (average 14.4%)，illite mixed layer and illite.The average pore throat radius of the reservoir is 0.26 micron，and the connectivity is poor and the irreducible water saturation is high.The reservoir is characterized by strong water sensitivity and easy water locking.The salinity of fracture fluid is less than 22 500mg/L，which can cause salt sensitive damage.The damage rate of fracturing fluid can be reduced from 39.5% to 28.5%.The water lock damage of the pre-fracturing fluid and the anti-expansion precipitation lock fracturing fluid system under the bound water saturation is compared，and the damage rate is reduced from 58% to 42%，and the recovery rate of 24h permeability of the gas drive core is 75.5% (prophase formula only 22.7%).The countermeasures of fast fracturing and quick release of fracturing fluid are put forward，including the use of less liquid volume，the whole liquid nitrogen injection，the drainage aid and the improvement of flow back pressure.This set of fracturing fluid system and technological measures have been applied in JS203-3HF and JS203-4HF two horizontal wells，with test production of 17.1×104m3/d and 20.760 8×104m3/d at 19.8MPa and 16.2MPa，respectively(with hydraulic pressure in the hydraulic channel of adjacent well gas test production of 3.845 8×104m3/d in 16.3MPa)，far exceeding the expectations of geology.The research results had provided technical support for the high efficient development of the gas reservoir.
Fractured low permeability carbonate reservoirs are triple porosity media with low porosity and low permeability，but there are natural dissolved vugs and natural fractures in the reservoir rock.Considering low speed non-Darcy seepage in reservoir rocks and stress sensitivity of natural fractures and acid fracturing fractures，a transient pressure behavior model of acid fracturing oil well in fractured low permeability carbonate reservoirs is established.Using logarithmic transformation and perturbation method，the transient pressure solution of real space is obtained，further，it analyzes the effect of low speed non-Darcy in reservoir rock，stress sensitivity of fractures，rock property improvement degree，flow channel improvement degree，acid fracturing area.The result shows the more obvious the low speed non-Darcy flow and stress sensitivity is，the more warping and bending the type curve is.The model can be used to evaluate the effect of the acid fracturing and evaluation of unstable productivity on carbonate reservoirs，identification and judgment of acid fracturing area and acid fracturing degree is of guiding significance to oil well increasing production measures，such as repeated fracturing，acidification and plugging，in fractured low permeability carbonate reservoirs.
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