ĐÁNH GIÁ TIỀM NĂNG THẤM CHỨA DẦU KHÍ TRẦM TÍCH ĐIỆN TRỞ THẤP LÔ 16-1 BỂ CỬU LONG ttta

TÓM TẮT NHỮNG KẾT LUẬN MỚI CỦA LUẬN ÁN:  Nghiên cứu tầng chứa điện trở suất thấp mỏ TGT thuộc lô 16-1 bể Cửu Long mà luận án đã đề cập hệ thống các phương pháp đánh giá độ bão hòa nước dựa trên tài liệu địa vật lý giếng khoan và mẫu lõi cho tầng chứa dầu khí điện trở suất thấp và có sự kiểm chứng bởi kết quả đo dòng và kết quả khai thác thực tế.  Đưa ra các nguyên nhân gây ra điện trở suất thấp: điều kiện kỹ thuật giếng khoan, điều kiện địa chất tại khu vực nghiên cứu. Trong đó nguyên nhân chính gây ra điện trở suất thấp là sét phân tán, vỉa mỏng và chiều sâu đới ngấm lớn.  Xây dựng được phương pháp luận nghiên cứu tham số độ bão hòa nước và độ thấm tuyệt đối của vỉa chứa dầu khí trầm tích điện trở suất thấp phục vụ cho công tác đánh giá trữ lượng dầu khí tại chỗ và công tác lựa chọn các khoảng mở vỉa thích hợp trong giai đoạn khai thác.  Xây dựng được hệ phương pháp nghiên cứu đặc tính thấm chứa chứa trầm tích chứa dầu khí điện trở suất thấp, đặc biệt độ bão hòa nước, chiều cao cột dầu và độ thấm tuyệt đối có thể áp dụng cho các đối tượng trầm tích điện trở suất thấp tương tự.  Xây dựng được mối quan hệ chặt chẽ giữa độ rỗng và độ thấm tuyệt đối theo tướng đá và đây là tiền đề để xây dựng mô hình thủy động phục vụ công tác dự báo sản lượng và quản lý mỏ.

MINISTRY OF EDUCATION AND TRAINING HA NOI UNIVERSITY OF MINING AND GEOLOGY BUI HUU PHUOC EVALUATE POTENTIAL PERMEABILITY AND STORAGE FOR HYDROCARBON IN THE LOW RESISTIVITY RESERVOIR BLOCK 16-1 CUU LONG BASIN Major: Geological Engineering Code: 9520501 SUMMARY OF TECHNICAL DOCTORAL DISSERTATION HA NOI- 2021 The dissertation is completed at: Department of Petroleum Geology, Faculty of Oil and Gas, Hanoi University of Mining and Geology Scientific Supervisors: Assoc Prof., Dr.Le Hai An Assoc Prof., Dr.Hoang Van Quy Reviewer 1: Dr Pham Van Tuan Hanoi University of Mining and Geology Reviewer 2: Assoc Prof., Dr Hoang Van Long Vietnam Petroleum Institute Reviewer 3: Dr Dang Ngoc Quy PetroVietnam Exploration Production Corporation The dissertation will be defended before the Academic Review Board at the University level at Hanoi University of Mining and Geology at : of date month .year The dissertation is available at the: - National Library of Vietnam - Library of Hanoi University of Mining and Geology INTRODUCTION Currently, hydrocarbon is produced mainly from the Granitoid fractured basement of Pre-Tertiary, the secondary productive targets are lower Miocene and Oligocene reservoirs Although being secondary productive hydrocarbon objectives, the lower Miocene reservoirs belonging to the Bach Ho formation and the upper Oligocene belonging to the Tra Tan formation have the best permeability properties of the Cuu Long basin But one of the biggest difficulties for geologists and geophysics is that the hydrocarbon bearing reservoirs have low resistivity and are occupying a large proportion in some fields of Te Giac Trang, Hai Su Trang, Rong… This has caused a lot of difficulties in identifying and evaluating reservoirs for the development and reservoir management Block 16-1 was discovered hydrocarbon at Te Giac Trang field in 2002 and the first oil flow was brought in the production line in 2010 Currently, the Te Giac Trang field in Block 16-1 is being produced with a flow rate of about 20,000 barrels of oil per day There were times when the peak yield is up to 55,000 barrels of oil per day from two main targets which are the Upper Oligocene (C sequence) of the Tra Tan Formation and the Miocene of the Bach Ho Formation (ILBH5.1/ILBH5.2) From the results achieved during producing and research has been opened a new premise, changing the concept of methodology to evaluate the oil and gas potential for the hydrocarbon in low resistivity reservoirs The sediments of the Tra Tan and Bach Ho Formations are mainly deposited in the environment of chanel, lakes and rivers into the shallow marine Because of the complexity of sedimentary facies, the complex distribution of clay minerals, electrically conductive minerals, thin beds, lamination has caused low resistivity of the oil reservoir leading to difficulties in determining the hydrocarbon saturation as well as the effective thickness of the reservoir containing hydrocabon of the lower Miocene, Upper Oligocene (C) With traditional method to evaluate hydrocacbon saturation parameter, there are still some limitations such as: the effect of low resistivity of reservoir is not excluded; the influence of minerals is unevenly conductive mineral along the well, dispersed clay in the reservoir Therefore, the author has chosen the research topic: "Evaluation of hydrocarbon permeability potential of low resistivity reservoir Block 16-1 in Cuu Long basin" The results of this study are the premise for the assessment hydrobacbon in place and reserves, planning perforation stratergy in the development phase and reservoir management Overview of the previous researches and the new issues posed by this research compared to previous studies Overview of researches on hydrocarbon containing in low resistivity envirement 1.1 Situation in the country Research on hydrocarbon in lowresistivity reservoir by MSc Nguyen Phuong Thuy and some articles by Assoc Le Hai An, Associate Professor Nguyen Van Phon, PhD Cu Minh Hoang, PhD Le Trung Tam and VPI Petroleum Institute In general, these studies have shown the causes low resistivity of hydrocarbon beaing and how to evaluate reservoir parameters These above studies evaluate the water saturation of reservoir reservoir but still mainly based on the deepth resistiviy curve and the ultrasonic curves (Vp / Vs, DTC) The researches of operators be worked/working on exploration and production phases in Cuu Long basin such as VietsovPetro, Petronas, Cuu Long JOC, have been conducted but still very difficult to apply to different areas due to the different geological conditions, different sedimentary environment, the influence of clay mineral components, containing rock composition is not the same Besides, individual studies have not had a comprehensive study to find providing optimal solutions to evaluate low resistivity sediments of hydrocaboean bearing zones Therefore, hydrocarbon containing low resistivity reservoir in Cuu Long basin is still a big challenge for geologists, geophysics, and geocientist especially in Block 16-1 - the area where the researcher is studying 1.2 Research situations in foreign countries Schlumberger Petroleum Services South East Asia studied a method for detecting hydrocacbon in low-resistivity reservoir, Pierre Berger et al and the authors review the causes of low resistivity due to: fluids with low resistivity, large bound water volume, and building resistivity to water saturation correlation based on core samples The researches published in the prestigious oil and gas journal SPE, Onepetro mainly focus on the study of the petrography, the clay contents, the lamilated clay in the reservoirs, the conductive minerals that contained in the hydrocarbon bearing zones, thin beds and reservoir containing micro porosity Application of nuclear magnetic resonance measurement method, high resolution of wireline resistivity measurement and resistivity measurement while drilling have been applied to improve the accuracy level when assessing hydrocarbon saturation parameter of reservoir The traditional calculation methods using the model (Archie, Simandoux, Indonesian, Dual Water, Waxman-Smits ) to calculate the water saturation parameter for the hydrocarbon reservoir, however, cannot rule out the effect due to the low resistivity of the reservoir The studies have shown the causes affecting the resistivity of the hydrocarbon reservoir such as: conductive minerals, clay type, clay distribution, formation water saltlity concentration… Although these reasons have been considered during the interpretation of well logs, the accuracy of the reservoir parameters are calculated: porosity, water saturation, permeability have not fully reflected the actual production status of field The identification of a new methodology system to calculate the water saturation parameters of hydrocacbon reservoirs for hydrocarbon initial in place, reserve calculations and simulation modeling is very necessary and urgent Thus, the studies listed above have shown the causes of the low resistivity of the hydrocarbon reservoir, but the water saturation calculations have not been verified by the results of measuring the water saturation of the core sample as well as cross-checked actual flow measurement results The postgraduate will go in the direction: Researching the cause of the hydrocarbon reservoir with low resistivity and then finding a solution to be precise the water saturation and absolute permeability of the research targets The results of water saturation and permeability calculated for hydrocacbon reservoirs are verified by the actual well performances and zonal contribution at perforated intervals The research purpose of the dissertation Study the nature of causing low resistivity of hydrocarbon reservoir and accurately evaluate their reservoir parameters such as effective porosity, especially water saturation, oil column height and permeability which basis for calculation of hydrocarbon initial in place and then serving field development planning Objects and scope of the study Research objects of lower Miocene sediment under Bach Ho formation (sequence BI.1) and upper Oligocene sediment (C) of Tra Tan formation Block 16-1 of Cuu Long basin, continental shelf offshore Vietnam The scope of research includes the studies of field geology, the studies of the depositional environment, well logs, petrography, conventional core analyisis, special core analysis, and the studies of the initial reservoir pressure Research contents This research is focused on clarifying some of the following issues: - Analysis of factors is the causes of the low resistivity containing hydrocarbon - Determine a system of methods for calculating water saturation for hydrocarbon reservoirs with low resistivity in lower Miocene (BI.1 sequence) and Upper Oligocene sediments (C sequence) in the Block 16-1 of Cuu Long basin - Determine the permeability, storage characteristics of low resistivity reservoir containing hydrocarbon and then evaluate their permeability, storage potential at Block 16-1 of Cuu Long basin Methodology of this study This dissertation is conducted mainly based on geological-geophysical, well logs data also combined with analysis results of petrography, conventional, SCAL, actual flow profile, well test data and surface measurement of the drilled wells in block 16-1 of Cuu Long basin currently operated by Hoang Long Hoan Vu company where the postgraduate is directly working and studying The research methods used in the dissertation are theoretical research methods combined with practical research methods as following: - Analyzing the causes of low resistivity in research area - Analyze and evaluate reservoir parameters: water saturation, oil column height, permeability - Analyzing the porous vs permeability relationship of the core sample based on depositional facies Scientific and practical meaning of this dissertation Scientific meaning: Giving the main causes of low resistivity for the hydrocarbon reservoir and give the rock-containing model of the research area at Block 16-1 Building a research methodology for low resistivity reservoir contain hydrocarbon to calculate parameters of storate and permeability which applied to Cuu Long basin Practical meaning: Propose a method to identify hydrocarbon reservoirs with low resistivity to avoid omission and create a basis for grouping, sumup or separate hydrocarbon reservoir in the study area This is the premise for the selection of reservoir opening and reservoir stimulation in order to improve the oil recovery factor in the production phase Select the best perforated intervals, group reservoirs that can be produced commingly, predict the water cut and oil production rate when perforating hydrocarbon bearing zones Provide results of calculated saturation, permeability, and height of the oil column which are input data for hydrocarbon initial inplace estimation and forecasting initial oil and water rates of perforated intervals for production wells of TGT field, Block 16-1, Cuu Long basin Provide results of calculated water saturation, permeability and these input data are basis inputs for building dynamic model, TGT field development plan, Block 16-1, Cuu Long basin Primary arguments of this dissertation - Argument 1: The cause of the low resistivity of hydrocarbon reservoir in the study area: the deep invasion zone of the drilling fluid and dispersed clay - Argument : Interrelate porosity and permeability correlation has a close relationship with depositional facies of low resistivity hydrocarbon reservoir: absolute permeability is used to assess water saturation (Sw) based on classification of rock types into classes according to the absolute permeability range then determine the water saturation (Sw) according to the oil column height (h) and the J-function function - Argument 3: The storage, permeability potential of low-resistivity hydrocacbon reservoirs of the study area is reflected through parameters (K, Sw, h), the change according to the rule: potential of hydrocarbon storage and permeability in the Northern part of the field is very good and decrease gradually downward to the Southern part The new highlights of this dissertation - The research on low resistivity hydrocarbon reservoirs of TGT Field in Block 16-1 of Cuu Long basin The dissertation mentioned the systematical methodology of water saturation evaluation based on well logs data and core samples for low resistivity hydrocarbon reservoir and is verified by production logging results and actual well performance - Conculede causes of low resistivity hydrocarbon reservoir in the study area are: technical conditions of drilled wells, geological conditions In which, the main cause of low resistivity hydrocarbon reservoir is dispersed clay and the large mud invasion zone - Developed a research methodology for the parameter of water saturation and absolute permeability of a hydrocarbon containing low resistivity reservoir to assess the estimation of hydrocarbon initial in place and reserve and the selection of appropriate hydrocarbon intervals to perforate in the production preriod - Develop a research methodology system for sediment-containing properties of low-resistivity hydrocarbon-containing sediments, especially water saturation, oil column height and absolute permeability that can be applied to sedimentary objects which is similar to low resistivity - Build a close relationship between porosity and absolute permeability classified by depositional facies and this is a prerequisite for building hydrodynamic models to predict production profiles and reservoir management Data base basis of the dissertation The resources used in the dissertation of the research subject in the existing block 16-1 of Cuu Long basin where is operated by Hoang Long Hoan Vu joint operating company that the postgraduate is directly working with and researching are following: Seismic data includes structural depth maps of main horizons which are ILBH5.2U, ILBH5.1 and Oligocene C used for this research The well logs data of eight (8) exploration wells and three (3) development wells include numerical documents of the conventional well logs, image well logs Formation Pressure data of six (6) exploration wells and development wells Core sample analysis data of six (6) exploration wells included depositional environmental analysis, conventional and special analysis Flow test and production logging survey of two developed wells Fluid sample analysis data of six (6) exploration wells Cutting sample data: petrography, mineral composition of six (6) exploration wells CHAPTER 1: OVERVIEW OF PETROLEUM GEOLOGY IN THE STUDY AREA 1.1 Location of research area The study area is located in the center of the basin which is part of the Cuu Long basin, off-shore continental Vietnam 100 km from Vung Tau The location of research aera is illustrated in Figure 1.1 Figure 1.1 Location map of study area Source: TGT full fill development plan 2010 1.2 Geological characteristics In general, the stratigraphic and sedimentary environmental explanations for the TGT Field are consistent with the general stratigraphic features of the Cuu Long basin such as the lower stratigraphic column The main research object of the dissertation is C and BI.1 sequences which belong to upper Tra Tan formation and lower Bach Ho formation Upper Oligocene - Upper Tra Tan sub-formation (C Sequence- E32 tt) Upper Tra Tan sub-formation - Upper Oligocene lies unconformity with the Bach Ho formation and identified by a brown, thick dark brown clay are on the top of sub-formation The thickness of this sub-formation ranges from 440-500m, the deposited clay of the upper Tra Tan formation have very high organic matter content and are the main source rock of oil generation in the TGT field Correlating with the seismic documents, the upper Tra Tan sub-formation belongs to C sequence According to the analysis results of well logs and geochemical analysis, the upper Tra Tan sub-formation has the medium porosity, permeability and this formation is both source rock, storage Lower Miocene - Lower Bach Ho Sub-formation (Sequence BI.1- N11bh) The lower Bach Ho sub-formation is subdivided into three smaller sets: ILBH5.2, ILBH5.1 and ULBH Lower Miocene - lower part of lower Bach Ho formation (ILBH5.2) The ILBH5.2 set is formed by sandstone and interbeded by gray siltstone and claystone The ILBH5.2 sub-sequence is deposited in the environment of rivers, lakes, transitional between freshwater and brackish water The thickness of the ILBH5.2 set fluctuates in the range of 370-490mTV This is the main hydrocarbon storage in the TGT field and is being produced in all blocks of the TGT field According to the analysis results of well logs, core sample analysis, this reservoir belonging to the ILBH 5.2 sub-sequence and have very good porosity, permeability which are consistent with the diagram of well performances being produced at this subject The general stratigraphic column of the Cuu Long basin (Figure 1.2) is correlated to the seismic sequences and the stratigraphic column of the study object is shown in the figure below Figure 1.2 Stratigraphy Colunm of Cuu Long Basin Source: Tran Nhu Huy’s Dissertation, 2016 1.2.1 Stratigraphy of TGT Field The TGT field is divided by a transverse fault system in the NorthwestSoutheast direction The fault slip surface tends to pour southward and gradually deepen Tectonic activities of faults strongly developed during the Oligocene and Early Miocene period and divided the field into multi-blocks H1 to H5 The seismic cross-section in the North-South direction is illustrated in Figure 1.5 North South Figure 1.5 North-South seismic cross-sections over TGT structures Source: Report on development plan of Te Giac Trang Field, 2010 In the direction from north to south, the structure of the TGT field has a stepwise shape that is shallow to the north and deep to the south Northeast-southwest tectonic faults have divided the TGT field into many separate blocks or compartments The oil-bearing reservoir tends to deepen to the south of the field, along with the tendency of sand layers to thin south and have less permeability Typically, the ydrocarbon reservoirs of the TGT field are quite thin due to being interbeded by clay layers, causing the reservoir of the TGT field to have many oil - water contacts as well as many hydraulic systems 1.2.2 Correlate and sub-divide reservoir units Correlating and dividing reservoirs are based on two main methods: stratigraphic time and stratigraphy and combined with pressure The subreservoirs or units are correlated together based on the pressure of the system The formation pressure has shown that between the layers of the TGT field there is a sudden change in pressure and divided into different hydraulic systems The reservoirs contain mostly vertical disconnections and in large sequence These reservoir units are divided in details by formation pressure 12 Mineralized concentration of reservoir water The formation water salinity has the ability to conduct electricity and reduce the resistivity of the reservoir The reservoirs of the TGT field often have the concentration of salinity ranges from 20kppm to 32kppm in the lower Miocene and 20kppm26kppm for the upper Oligocene and this is completely consistent Figure 2.3 Dispered clay observed at with general geology of conventional core slaps Cuu Long basin The ratio of connate water - bound water Connated water is membrane bound water surrounding the mineral grains that surrounded sands and clay Montmorilonite clay has a large surface area Cation exchange capacity of these clay minerals is very large, resulting in low resistivity Research object, Montmorilonite clay content occupies a relatively large portion (Figure 2.4) is the cause of the low resistivity of the formation rock and reducing porosity properties Conductive minerals Minerals such as: Pyrite, Glauconite, Hematite, Graphite, Smectite, Illite, Chlorite, Kaolinite or conductive debris present in rock contain effect on the measured resistivity In the study area, in addition to clay composition, Pyrite conductive mineral is present and unevenly distributed along the wellbore with very low Figure 2.4 Portion of clay minerals of study content object 13 Thus, the presence of the above factors is the basic factor causing the low resistivity of the Miocene sedimentology of the study object: deep infiltration zone, thin bed layer with dispersed clay CHAPTER 3: RESEARCH METHODOLOGY FOR HYDROCARBON IN THE LOW RESISTIVITY RESERVOIRS In this dissertation, three reservoir parameters are studied: effective water saturation Sw, oil column height (h) and absolute permeability (K) 3.1 Height of oil column Oil column height is defined as the absolute height from the water oil contact to the top of the reservoir Oil column heights are determined by three basic methods: half way concept, the Oil Down To and formation pressure interpretation method Well-A With DST Well-B Well-B Well-A No DST Crest Crest P1 h ODT h P2 Fault Fault ODT P2 ½ way ½ way P3 WUT or Spill P3 WUT or Spill Figure 3.1 Oil column height and reserves classification Thus, the two methods in Figure 3.1 have a large uncertanties because the oil-water contact is assumed which is based on the accuracy of the map and how to take the structural spill point In this dissertation, the oil column height is a parameter that is focused on research with a new methodology Determine the height of the oil column by the Excess Pressure justification method, which is a highly accurate method of determining the oil water contact with excellent accuracy and is suitable for low resistivity reservoir, thin beds, sand inter bebed by clay and stacked oil sands as figure 3.2 Figure 3.2 Oil column height determined by Excess pressure and reserve classification 14 đối ((m) sâu tuyệt (m) Độ TVDss (m)((m) TVDss tuyệt đối Độ sâu 3.2 Method of determining the height of oil column Áp suấtPressure dư Áp suất thành hệ Formation Pressure Excess There are many methods to determine the oil column Áp suất đo điểm heights However, in this dissertation, the reasercher only mentions the Excess pressure Áp suất method The Excess pressure dư plots are constructed by the defined density value and the Excess pressure value at the Đường nước datum depth points The Excess pressure at the formation water Figure 3.3 Conversion of graph of reservoir is equal at different normal pressure to residual pressure depths Figure 3 Traditional pressure-depth charts make it difficult to discern free water levels However, the oil water contact can all be identified clearly by using the Excess Pressure Plot The point of intersection between the lines of water and oil is the depth of free water level (FWL), because at this depth the oil and water pressures are the same CHAPTER 4: PREDICT ABSOLUTE PERMEABILITY AND WATER CUT OF RESERVOIR IN STUDY AREA 4.1 Predict absolute permeability Model of sedimentology deposition In general, the stratigraphy and sedimentary environment of the TGT field lies in the general background of the Cuu Long basin Based on geological, geophysical and conventional core descriptive analysis, the research object is sequences BI.1 and C of lower Miocene and upper Oligocene deposits of TGT which is deposited in two main environments Alluvial plain and Lacustrine (lacustrine) Depositinal facies are analyzed based on core samples/ core slaps and then combines with image logs and well logs data are used to analyze sedimentary facies along the well bore The depositonal facies of the TGT field are coded as follows: Table 4.1 Assign depositinal facies with code Depositional Enviroment Lacustrine Facies Gravity Flow Hyperpycnal Trangresive Mouth Bar Sandflat Lake Shoreface Lake Mud Abbreviation Facies Code GF HY TR MB SFT LS LM 15 Depositional Enviroment Facies Soil Overbank Crevasse Splay Channel Sheet Flood Alluvial plain Abbreviation Facies Code SO OB CS CH 10 SF 11 Each RCA core sample point is assigned a certain facet type based on the sampling depth The depth of the core samples were adjusted to match the depth of well logs to coincide with the depth The relationship between porosity and permeability is built on a core sample and is then computed along the well This relationship is corrected with the actual current measurement results during the flow test and the actual well performance 4.2 Predict water cut when perforating hydrocacbon zone To predict the water cut before perforating the hydrocarbon zones base on input parameters water saturation and permeability and the relative permeability is the necessary factors to be used 4.2.1 Relative permeability The relative permeability used in this dissertation is an important input parameter to predict reservoir water cut before perforating the reservoir Predicting the water cut before opening hydrocarbon reservoir is a very important factor 4.2.2 Relative permeability of core sample 1.0 RT5 0.9 0.8 K