Lithology Identification And Formation Evaluation In The Deep Dongling Region, South Of Songliao Basin

There are many areas where have been found volcanics, in some of which are the better palce of igneous reservoir for oil and gas production.By prospecting in the earlier stage, it was proved that the mid-and-deep volcanitcs were the significant reservoirs in Mesozoic of the south of Songliao Basin. There is a good prospect in the future. Prognositc reservs and controlled reserves have been provided.Because of deep embedding of volcanics and the lack of outcrops in the Songliao Basin, There are not a few drilling wells that touch any volcanics. So there were little samples. Consequently, it is very short of samples of volcanics. Since the lack of volcanic cores, the information is not provide including the distribution of lithology, period, cycle, attitude, lithophases, structure etcs. It is not explicit that the range of volcanics distribution and lithphases are divided and the reservoir type and natural gas source are not understood. These issues affecte badly the exploring and prospective value of volcanic gas in the deep of Songliao basin. So it is difficult problem in the subject at present.For the prediction of volcanic reservoir, the colleagues of both here and abroad have been made many relative predicts. Due to singularity of approach , multi-solution and low accurate predition, there is still no mature methods to meet the needs of prospection of volcanics reservoir.Therefor, based up on the basic principle of volcanic petrology combined with the integrated study of multiple knowledge, this paper, instancing the Dongloing Fault Depression of the south of Songliao Basin, has studied deeply the approaches of predition and evaluation of volcanics reservoirs with the information of core and well log etc.一. Well logging technical study of volcanics identification Volcanics identification is the base of studying volcanics reservoir. The straight and effective methods of identification of volcanic lithology are core analyses. Due to the lack of sampling, it is necessary to use well log to identify the lithology.1. Well log characteristics of volcanics response Correlated the individual log curves of Dongling Area on this paper, it is summarized that there were below principles of response in the area.(1) It is transited from basicty to acidity in lithology, and radioactivity is gradually increased. it is presented that the value of natural gamma ray is low, andisite is middle and ryyolite is high in this area(2) The response of neutron log is gradually decreased from basicty to acidity pass through neutral. It is presented that : 10～22% of basalt, 7～21% of andesite, 5～12% of rhyolite. Since alteration of eruptive tuff becomes clay mineral adsorbed formation water with high value of neutron log, it approaches 24%.(3) Due to the decrease of Fe, Mg minerals density, density logging is decreased from basite to acidite pass through neutral. (4) It is different from the other lithology that the eruptive tuff has characteristics with high acoustic slowness (300μs/m)and low resistivity (5-50Ω.m).2. The features of volcanics crossplotsCrossplot of well logging is the effective method to indentify the Igneous lithology of the basin bearing gas and oil. The distribution of lithology on the crossplot is showed visually, then volcanics could be identified clearly. In studying, based on the named result of 100 core samples of 15 wells, we analyzed systematically the response of measured well logging. The crossplot of natural gamma ray vs. resistivity was drawn up. Three classes and seven kinds of volcanics were divided.3. Technical study of lithology identification using imaging well logging The Igneous lighology of deep Dongling is complicated. There are developed from acidity to neutrality and basicty. There are seven kinds of lithology at present.Using conventional well logging, the lithology could be divided with classes. And combining with imaging that reflect texture and structure, the lithology could be identified and divided further. Since imaging log is the integrated response of resistivity and reflected sonic of the geological bodies with multiresolution, so it is impossible to identify the standard geological pattern from the geolithology. In the studing, based on the standard databaseof geological pastern, the information of imaging was calibrated. Considering the characteristics of the texture and structure of rocks, 8 kinds of standard imaging pattern was build up.二. Four charateritics relationships and qualitative identificaiton of hydrocarbon reservoir 1. Four charateritics relationships of volcanicsStuding of four charateritics relationship of volcanics, the Igneous lithology, lithophases, electricity, and oil-gas-bearing property vs. physical property of reservoir were fixed on.It is considered after study that the physical property is controlled with lithology obviously. The relationships among oil-gas-bearing property and physical property vs. lithology are closely. It is provided the geological evidence to establish the log interpretatiing model of reservoir parameters.2. Qualitative identificaiton of hydrocarbon reservoir Through detailed analysis of the four characteristic relationship and synthetically processing the basic data synthesisly, it was established to identify the oil and gas reservoir of Dongling Field. This paper has basically used three methods:ΔlgR,crossplot and oil ,gas and water layers distinguishing index to identify the hydrocarbon reservoir.三. Overall evaluation of volcanic reservoir1. Establish of mineral modelThis paper has established mineral model based on the ideas of quantitative division(QAPF). The main mineral components werer divided into five groups: quatz(Q), felstone(F), alkali feldspar(A), plagioklas(P)and ferromagnesian mineral(M). Because quatz and felstone cannot be coexisted, the pratical mineral combination are individually Q,A,P,M or F,A,P,M four groups.Q——quatz(quatz,cristobalite, christensenite);A——alkali feldspar[orthoclase, anhydrous scolecite, anorthoclase, eisspath and albite(An0-5)];P——plagioclase(An4-100) and arcticite; F——felstone;M——Ferromagnesian and related minerals[anthrophyllite,hornblende, octobolite,olivine, opaque minerals, accessory mineral(such as zircon, arpidelite, agustite), acanthicone, garnet, melilite, calcio olivine etc.].2. Igneous petro-physical log evaluation——Simple Depend on mentioned previously principle of process and interpetatoin of igneous well log data, the system of Simple(System of Igneous & Metamorphic Petro-physical Log Evaluation) was programmed under the WINDOWS. Using thoughts of object-oriented program designing, based on the content selected from the menu, the methods were decided to process. The selection of various paratmeters, modification and the procedure of process were dealt with dialogue box. The operation is simple and easy. Theerefor it is named as Simple. It is not only to process the log data of igneous reservoirs, but also to pre-process and manage the data. Because of the similarity between a good many aspects of complexity of mineral components and density of lithology of metamorphics and igneous, the many aspects of this software can be used into the layers of metamorphics.3. Soft ware application of multi-component processing"Double-component model"is the model to analyze formation components of complex igneous with fissure and to calculate parameters of porosity, saturation of fissure, porosity and saturation of base block, and total porosity and saturation, etc.Based on the results of analysis with application of the software, the computed porosity and the porosity interpreted from cores are consistent. With the issues of the selection of parameters and saturation equation( lack of knowledge of electric conduction in laboratary), there was a difference between the results processed with saturation and the conclusion of the test..四. Principles of igneous phases and the distribution of oil and gas in space1. The features of distribution of igneous phasesLithophases of igneous are mainly ffusion and eruption phases, there is a few phasese of volcanic conduit. In the eastsouth and eastnouth, thick ffusion phase developed. In the middle area, inter-bedding of ffusion and eruption phases distributed. Volcanic conduits phase are mainly thin inter-bedding developed shown in the wells of SN116, SN182 and SN187.2. The distribution features of igneous hydrocarbon reservoirUnderstanding of igneous lithologyThe lithology of Formation K1yc is singularity, which mainly is a suite of acidity rhyolite. This layer distributes all over the area. The thickness around westsouthen well SN115 and eastnothern well DK189-2 is thick, above 100m. The lithology of Formation J3h mainly distributes with andesite, basalt and tuff. In this area, it develops a suite of tuff layer inter-bedded with a thin rhyoite with tectonic activity except the area of SN111 and SN188. There is a thick andesite layer in the other part in the base, and the upper is a suite of basalt, and the upper most was covered with thin andesite, in which there some are thin tuff.Situation of developing porosity of igneousThere is a thick andesite zone in the southwest of the area, which porosity is high and mainly above 10%. To the northwest, andesite is thinned gradually, and basalt appears with mainly basalt and andesite inter-bedding, which porosity is of above 10%. Affect with clay, some layers are lower than 5%. So the porosity of andesite zones is higher than the porosity of basalt zone slightly. Around the well of SN111 and SN188, due to tectonic activity, there developed a suite of tuff, which enables the porosity lower about 5%.3. The relationship between igneous phases and hydrocarbon distribution.Effusion phase develops thick in the southwest, the hydrocarbon distribution is wide; towareds the northwest, effusion phase and eruption phase are inter-bedded spreading throughout., hydrocarbon distribution is poorer than southwest; Around the well of SN111 and SN188, due to tectonic activity, there developed a suite of tuff, in which zone the hydrocarbon distribution is poor.