GB/T 31456-2026Technical specification for surface geochemical exploration for oil and gas (English PDF)

4.1 General Survey

4.1.1 Evaluation Object Sedimentary basins or depressions with limited exploration.

4.1.2 Work Tasks Investigate and study regional geochemical characteristics and regional anomaly zones, and combine geological and geophysical data to predict the distant oil and gas potential of basins or depressions. The scene provides a basis for early evaluation.

4.1.3 Sampling Density For area measurements, the distance between sampling points and the distance between sampling points should be less than or equal to 10 km. For profile measurements, the distance between sampling points should be less than or equal to 10 km.

4.2 Census

4.2.1 Evaluation Object Basins, depressions, or zones with potential for oil and gas production.

4.2.2 Work Tasks The investigation and study will determine the regional geochemical background and anomaly characteristics, delineate favorable oil and gas accumulation zones, and provide a basis for detailed seismic surveys and parameter well location. Provide evidence.

4.2.3 Sampling Density Network sampling is performed with line spacing less than or equal to 1 km and point spacing less than or equal to 1 km.

4.3 Detailed Investigation

4.3.1 Evaluation Object Favorable oil and gas accumulation areas or favorable traps determined by geology and seismic activity.

4.3.2 Work Tasks Investigate and study the concentration, combination characteristics, anomaly morphology, and distribution direction of surface geochemical anomalies, combined with petroleum geology and geophysics. The data were comprehensively evaluated to select the best traps, providing a basis for the deployment of exploratory wells.

4.3.3 Sampling Density Sampling should be performed using a grid with a line spacing of

0.5 km or less and a point spacing of

0.5 km or less. The area of the background zone for measurement should be [area missing]. The area is 3 to 5 times the size of the target area.

4.4 Detailed Investigation

4.4.1 Evaluation Object A trap for expanding oil and gas reservoirs or for unexplored oil and gas potential reservoirs.

4.4.2 Work Tasks Investigate and study the geography between discovered oil and gas reservoirs and their surrounding areas, or between traps with existing oil and gas discoveries and adjacent unexplored traps. Similarity in chemical anomalies can be used to predict oil and gas extents or select optimal drilling targets, and this can be combined with geological, drilling, and geophysical data for comprehensive analysis. Evaluation serves as a basis for the expansion and rolling exploration of known oil and gas fields or for the deployment of evaluation wells.

4.4.3 Sampling Density Sampling should be conducted using a grid with a line spacing of

0.25 km or less and a point spacing of

0.25 km or less. The area measurement range should cover the background area. The area should be 3 to 5 times the area of the target area.

5.1 Data Collection

5.1.1 Latest topographic map, geological map, stratigraphic columnar section, structural map, and fault distribution map of the work area.

5.1.2 Aerial and satellite photographs.

5.1.3 Gravity, magnetic, electrical, seismic, and geochemical data.

5.1.4 Drilling data.

5.1.5 Regional geological survey reports, research reports and related literature.

5.1.6 Geological, hydrological, geochemical landscape and meteorological data.

5.1.7 Natural geography, transportation and social environment data.

5.2 Site Survey

5.2.1 Understand the natural economic geography, topography, transportation conditions, and distribution of settlements in the work area.

5.2.2 Select 3 to 5 test sites in each geochemical landscape area.

5.2.3 Soil and gas samples were collected from different lithological sections below the surface disturbance zone at each test point, with longitudinal sampling intervals of less than 0.5m.

5.2.4 The samples were analyzed according to the test items in

6.3.1 and 6.3.3.

5.2.5 Determine the sampling depth, stratigraphy, and lithology of surface geochemical samples based on the test and analysis results.

5.3 Construction Design

5.3.1 The construction design document should include. project background, geological tasks, preliminary tests, sample point deployment, sampling requirements, experimental testing items, and construction procedures. Quality requirements, work plan, organizational structure, safeguard measures, health, safety and environmental management, main technical equipment, budget, and expected delivery. Results.

5.3.2 If discrepancies are found between the design content and the actual situation during fieldwork, the design should be adjusted and modified in a timely manner.

5.4 Personnel Training

5.4.1 Before conducting field sampling operations, all personnel should receive job skills training to master sampling skills and clarify each person's responsibilities. Work tasks.

5.4.2 Before conducting field sampling operations, all personnel should receive emergency training on safety, environmental protection, and personal protection.

6.1 Sampling Point Deployment

6.1.1 Arrange the sampling points on the topographic map according to the design requirements, and locate the sampling points according to latitude and longitude or plane rectangular coordinates.

6.1.2 The sampling point movement error shall meet the following requirements.

a) The movement error of the preliminary survey points shall not exceed.200m;

b) The movement error of the survey points shall not exceed 100m;

c) The error in the movement of the detailed inspection point should not exceed 50m;

d) The error in the movement of the inspection points shall not exceed 10m;

e) If the designed sampling points are not feasible during construction, they may be moved within 25% of the distance between the survey line and the sampling points, and the relocation point should be noted. Reasons, direction of movement, and distance; if the movement range exceeds 25%, the design points should be modified or changed.

6.1.3 The location numbering shall meet the following requirements.

a) The area measurement points are numbered along the north-south direction, and are deployed from west to east; the deployment order of the points is from south to north.

b) The area measurement point number consists of the survey line number and the measurement point number, both represented by Arabic numerals. The survey line number comes first, followed by the measurement point number, with a separator in between. Connected by "-", it is marked as survey line number-survey point number, such as "12-86", which means the 86th sample point of the 12th survey line.

c) The profile measurement point number is marked with uppercase English letters and Arabic numerals, such as "A-16", which means the 16th sample point of profile A.

6.2.1 Soil Sample Collection

6.2.1.1 Sampling points should be located at least 20 meters away from the pollution source. Sampling points on slopes should be located on the uphill section of the pollution source, avoiding moving sand dunes, embankments, and other obstacles. Fill soil, recent natural deposits, or alluvial deposits.

6.2.1.2 Take samples using a twist drill, a Luoyang shovel, or a spade, according to the sampling depth and layer determined in 5.2.5.

6.2.1.3 The sampled material should be fine-grained sediments with basically consistent lithology, and gravel, tree roots, and grass roots should be removed from the sample.

6.2.1.4 The sample size should be no less than 500g.

6.2.1.5 Record and describe the sample information using a pencil. See Table 1 and Table 2 for the sampling record forms.

6.2.1.6 Sample packaging may be selected from one of the following methods.

a) Pack the sample at the sampling site with cellophane lined with kraft paper;

b) Seal the sample in cans or bottles at the sampling site;

c) Pack the samples in aluminum or tin foil bags at the sampling site.

6.2.1.7 Samples packaged according to methods 6.2.1.6a) and

c) should have an internal label with the location number, and the same number should be written on the outside; samples packaged according to method 6.2.1.6b) The samples should be labeled with the location number.

6.2.1.8 After sampling is completed, the sampling pit should be backfilled.

6.2.2 Rock Sample Collection

6.2.2.1 Remove the weathered layer and take samples from the fresh surface of the bedrock outcrop using a geological hammer or drilling machine.

6.2.2.2 Rocks collected from the same stratum should have basically the same lithology.

6.2.2.3 The sample weight should be no less than 500g.

6.2.2.4 Use a pencil to record and describe the sample information on the sampling record sheet according to the contents of Table 1.

6.2.2.5 Sample packaging may be selected from one of the following methods.

a) Pack the sample at the sampling site using cellophane or paper bags lined with kraft paper;

b) Seal the sample in cans or bottles at the sampling site;

c) Pack the samples at the sampling site using cloth bags lined with cellophane.

6.2.2.6 Samples packaged according to methods 6.2.2.5a) and 6.2.2.5c) shall have an internal label and an external number; samples packaged according to method 6.2.2.5b) The product should have a label with the location number affixed to it.

6.2.3 Water Sampling

6.2.3.1 Collect shallow confined water or unconfined water with uniform hydrodynamic conditions from domestic water wells within the work area.

6.2.3.2 Collect water samples from rivers, lakes, marshes, reservoirs, and springs.

6.2.3.3 The water sample volume should be no less than 1000 mL.

6.2.3.4 Water samples for analyzing soluble gaseous hydrocarbons and other organic components should be in glass bottles; water samples for analyzing inorganic components can be in polyethylene plastic bottles. bottled.

6.2.3.5 Record and describe the sample information using a pencil. See Table 3 for the sampling record form.

6.2.3.6 Each sample bottle should be tightly sealed, placed upside down, and labeled with a number.

6.2.3.7 Before taking water samples, rinse the cleaned bottle and stopper three times with the water sample to be taken. Different categories of test items should be sampled in separate bottles.

6.2.3.8 Water-soluble hydrocarbons shall be extracted on-site according to the method specified in GB/T 29173.

6.2.4 Gas Sampling

6.2.4.1 Gas collection device 6.2.4.1.1 All devices and containers used for collecting gas should be cleaned and free of contaminating gas components. 6.2.4.1.2 After sampling, record the sample number (well number), stratigraphic position, and depth information on a label and affix the label to the container.

6.2.4.2 Natural Gas in Oil and Gas Wells 6.2.4.2.1 Use a gas collecting cylinder for sampling. The volume of the gas collecting cylinder shall not be less than 1000 mL. 6.2.4.2.2 Use saturated saline solution as the sealing solution and take samples by water displacement method. 6.2.4.2.3 The bottle must be kept upside down during transportation and storage.

6.2.4.3 Soil gas 6.2.4.3.1 The gas extraction layer should be selected below the surface disturbance zone and above the water table. 6.2.4.3.2 In areas where the water table depth is greater than

1.0 m and there are no gravels or bedrock at depths shallower than

1.0 m, the drainage gas collection method shall be used to collect the soil gas. Free gas is collected in a gas collecting bottle. The volume of the collected gas sample should be no less than 10 mL. 6.2.4.3.3 Take soil or rock samples from the target stratum, break them into particles smaller than

0.5 cm, and place them in a brine bottle. Add saturated brine to the remaining space at the top. 50mL, immediately seal and invert.

6.3 Experimental Testing

6.3.1 The following items should be tested on soil and rock samples.

a) Acid hydrolysis of hydrocarbons shall be carried out in accordance with the provisions of GB/T 29173;

b) Pyrolytic hydrocarbons shall be handled in accordance with the provisions of GB/T 29173;

c) Headspace light hydrocarbons shall be handled in accordance with the provisions of GB/T 29173;

d) Physical adsorption of hydrocarbons shall be carried out in accordance with the provisions of GB/T 29173;

e) Polycyclic aromatic hydrocarbons shall be handled in accordance with the provisions of GB/T 29173;

f) Aromatic hydrocarbons and their derivatives shall be handled in accordance with the provisions of GB/T 29173;

g) Alteration carbonates (DeltaC) shall be processed in accordance with GB/T 29173;

h) Pyrogenetic mercury shall be handled in accordance with the provisions of GB/T 29173;

i) Trace elements shall be supplied in accordance with the provisions of GB/T 14506.30;

j) Radioactive elements shall be handled in accordance with the provisions of GB/T 16145;

k) Oil and gas microorganisms shall be handled in accordance with the provisions of SY/T 7471;

l) Stable carbon isotopes of hydrocarbons such as methane shall be handled in accordance with the provisions of GB/T 18340.2.

6.3.2 The following items shall be tested on water samples.

7.1.1 Substitution Method

7.1.1.1 When there are outliers in the geochemical analysis data of the work area, the substitution method shall be used for data processing.

7.1.1.2 When outliers in a certain geochemical index are determined to be caused by factors other than oil and gas leakage, the outliers should be removed, and the remaining data should be calculated. Replace outlier values with the mean or median.

7.1.1.3 When an outlier in a geochemical index is determined to be caused by oil and gas leakage, the outlier should be removed, and the mean of the remaining data should be used. Replace outlier values with 3 times the standard deviation.

7.1.2 Correction Coefficient Method

7.1.2.1 When a certain geochemical index data shows a significant correlation with one of the interfering factors among topography, soil lithology, and soil color, it is advisable to use... Correction is performed using the correction coefficient method.

7.1.2.2 Classify and statistically analyze the measured values of a certain geochemical index of all samples in the work area according to a certain interference factor.

7.1.2.3 Select the sample with the most interference factor and calculate its average value (Xi).

7.1.2.4 Calculate the average value (Xj) of samples for other interference factor categories respectively.

7.1.2.5 Calculate the correction coefficient (K0) using formula (1).

7.1.3 Regression Correction Method

7.1.3.1 A certain geochemical index data interfering with one of the following soil particle size distribution, moisture content, carbonate content, or organic carbon content. When there is correlation, regression correction is recommended.

7.1.3.2 Establish a univariate linear equation between geochemical index data and a certain interfering factor, as shown in formula (3).

7.1.3.3 Use formula (4) to correct the measured values of geochemical indicators for a single sample point.

7.1.4 Comprehensive Regression Method

7.1.4.1 When a certain geochemical index data is affected by multiple interfering factors such as soil particle size distribution, moisture content, carbonate content, and organic carbon content... When all factors show significant correlation, first perform single-factor quantitative correction to identify the primary and secondary influencing factors. Then, it is advisable to use a comprehensive regression method for correction.

7.1.4.2 Establish a multivariate linear equation for geochemical index data and various interfering factors, as shown in formula (5).

7.1.4.3 Establish the multiple regression correction equation, as shown in formula (6).

7.2 Screening of Geochemical Indicators

7.2.1 Calculate the correlation coefficients between each indicator, compile a correlation coefficient matrix table, perform a significance test on the correlation coefficients, and determine the correlation coefficients between each indicator. The degree of relevance.

7.2.2 Perform R-type cluster analysis on the data of each indicator, draw a cluster phylogenetic diagram, and determine the affinity between individual indicators and the combination of individual indicators. The degree of closeness or distance between them.

7.2.3 Perform R-type factor analysis on each indicator data to group the indicator variables into common factors. The principal cause is determined when the cumulative variance contribution is greater than 80%. Sub-projects calculate factor loadings and determine the combination characteristics of geochemical indexes on the principal factor axis.

7.2.4 Based on the analysis results of

7.2.1 to 7.2.3, determine 2 to 3 indicators for each geochemical exploration method according to the degree of correlation differences among the indicators. As a representative geochemical indicator of the study area.

7.2.5 If known oil and gas reservoirs exist in the study area, the geochemical indicators selected in

7.2.4 shall be used for verification, and the indicators that show a significant response to the oil and gas reservoirs shall be selected. Representative geochemical indicators of the characteristics.

7.3.1 Arithmetic Mean Method

7.3.1.1 When geochemical index data follow a normal distribution, the arithmetic mean method should be used to determine the background value.

7.3.1.2 Calculate the background value using formula (7).

7.3.2 Logarithmic Transformation Method

7.3.2.1 When geochem...