Chaluhe Basin is in Jilin Province of China with a cumulative sedimentary rock thickness of about 6000 meters and has four subdivisions: Wanchang Structural High, Bo-Tai Sag, Xinanpu Sag, Liangjia Structure High and the Gudian Slope. The basin with its better source rock distribution and more favorable maturation indicators than the adjacent Moliqing and Luxiang Basins is expected to be a potential hydrocarbon-producing basin. Four (4) wells were used in determining the maturation hydrocarbon generating potential of the mudstone beds present in the Eocene Formations (Shuangyang, Sheling and Yongji). Obtained result revealed heat flow average of 71.8 mW/m 2 , oil generation between 3.15 mg/g TOC and 39.49 mg/g TOC with gas generation of 6.98 mg/g TOC to 92.83 mg/g TOC. In conclusion the Eocene Shuangyang mudstone is the main petroleum source rock.
The Chaluhe Basin is one of the three basins in the Yitong Graben, namely Moliqing and Luxiang basins. It lies in the north of the Yitong Graben, and is located between the Changchun city and Jilin city of Jilin province and covers an area of approximately 1350 km2, with cenozoic sediments up to 6000 m (
Based on apatite fission track analysis of some few samples from Chaluhe Basin and basin modeling study, it can be concluded that since the Oligocene (36.6 Ma) in the Graben, the Chaluhe Basin has undergone two episodes of uplift during 24.9 - 19.1 Ma and 6.9 - 4.9 Ma, with an average apparent exhumation rate to be 70.34 and since 21.8 Ma. The results of thermochronological analysis can also be supported by the evidence from geological relationships such as geodynamics, volcanic activity, and stratigraphic division and correlation [
So far, more than 50 wells have been drilled in the basin. To date the overall exploration within the Chaluhe
Basin has not been very successful and only local hydrocarbon production has been discovered. In contrast, the Moliqing and Changchun oilfields have been found in the Moliqing and Luxiang basins in the SW part of Yitong Graben, with reserves of 3317 × 104 t oil and 13.29 × 108 m3 gas. The Chaluhe Basin has similar Cenozoic sediments and tectonic setting to the adjacent Moliqing and Luxiang basins, and widespread distribution better source rocks and more favorable condition of hydrocarbon accumulation which suggests that the Chaluhe Basin should have a great potential of hydrocarbons and can be considered as the prime targets for future hydrocarbon exploration within the Yitong Graben.
The Yitong Graben is a petroliferous late-Mesozoic and Cenozoic slip-extensional basin located at the north east of China between the cities of Changchun and Jilin. This basin makes part of the Tanlu fault zone which is one of the largest continental strike-slip faults in the world [
The formation and development of the Yitong Graben mainly resulted from the collision between the Indian plate and the Eurasian plate, and the subduction of the Pacific plate to the Eurasian plate [
The Yitong Graben consist of three basins namely, Chaluhe, Moliqing and Luxiang basins, and is an oil- bearing geological structure with unique characteristics in Northeast China. On the basis of apatite fission track ages and geological relationship, the tectonic uplift history of the Yitong Graben since the Oligocene was discussed. The results of thermochronological analysis can also be supported by the evidence from geological relationships such as geodynamics, volcanic activity, and stratigraphic division and correlation.
Evidence from geodynamics background suggests that the tectonic stress field of the Yitong Graben changed from tenso-shear to compresso-shear during the Cenozoic [
The materials and input data required to run the BasinMod 1-D of this study includes the present thicknesses of each stratigraphic unit, top and base wellbore depths, and the lithology mixes. Biostratigraphy is derived from the washing of ditch cuttings, sidewall cores and conventional cores which are then separated and analyzed for micro fauna (Foraminifera) and flora (spores and pollens) so as to ascribe a presumed age to each interval studied. Kerogen types, total organic carbon (TOC), kinetic algorithms and results of pyrolysis analyses, the location of wells, and organic thermal indicators include vitrinite reflectance values; the water-sediment interface temperatures [
Drilling, logging and paleontological studies reveal the Chaluhe basin contains seven different sedimentary rocks formations from the Eocene to the Quaternary with scattered Neogene formation in the Cretaceous and Jurassic outcrops, overlying a pre-tertiary basement (
For maturity calculation, a number of methods are available but the Lopatin TTI method is employed in this research.
The Time Temperature Index (TTI) method for calculating maturity is the Lopatin (1971) application of the assumption that the maturity reaction doubles for every 10 degree Celsius increase in temperature. This simple method has been widely used for basin modeling since it was popularized by Waples (1980). The TTI method provides reasonable prediction capabilities and direct empirical correlation to vitrinite reflectance (Ro), as well as to other measured maturity indicators such as TAI and TMAX. BasinMod provides several methods for conversion of TTI to %Ro. The user may select from the conversion constants of Goff, Hood et al., Issler, Royden, Waples, or Dykstra. The user may enter his/her conversion constants with the “User” option. Another alternative is to define the conversion of %Ro to TTI using the “Table” option. BasinMod accepts conversions for TAI and TMAX as well as a third maturity indicator which can be labeled by the user. Spore Color Index (SCI) or Conodont Alteration Index (CAI) is two of the other indices that can be used for TTI to %Ro conversion. Major companies usually have standard correlations for these indices.
Comprehensive analysis of the test drilling data shows presently high geothermal gradient in the Chaluhe Basin with 3.36˚C/100m (
Further analysis of the basin reveals geothermal gradient differences in tectonic units (
It is of essence to re-emphasize that, this study, as its topic clearly states deals only with one dimensional model of the source rocks (units) of the study area, being the Chaluhe Basin of the Yitong Graben.
Tectonic units | Well name | Present geothermal gradient (˚C/100m) | |
---|---|---|---|
Chaluhe Basin | Bo-Tai Sag | Chang 7 | 3.22 |
Wanchang Structural Belt | WC 1 | 3.44 | |
Xinanpu Sag | Chang 25 | 3.54 |
On the basis of geological studies, drilling, geophysical and analytical testing and other information on the history were combined with logging data to determine facies and eroded thickness, and seismic profiles, for calibration to model the burial history and sedimentary deposition in the basin (
1) Based on the burial and subsidence models of Wells Chang 7 and 8 (
Deposition rate and the rate of evolution of tectonic subsidence are consistency when the deposition rate is positive, the sedimentation rate is also positive, the deposition rate is negative, the sedimentation rate is also negative and also consistent with each other, but in this model, the size of the deposition rate and subsidence rate are inconsistent.
2) According to the burial and subsidence model of Well Chang 25 (
3) In
In sum, the Chaluhe of Neogene sedimentary strata deposition rate decreases, the settlement curve is relatively flat, the late Neogene uplift and erosion led to the shrinking of the basin. Presently, the layer depth is not the greatest geological history depth.
The transient heat flow model (Transit Heat Flow) is used to restore the geothermal evolution of the Yitong Graben, and use the measured temperature of the simulation results to be tested and calibrated. The ancient geothermal evolutionary history of well Chang 7 for example (
In the evolutionary history of the geothermal gradient, as mentioned above, the overall performance is; since historical times, with the settling basin, filling, each faulted historical geothermal gradient decreased. In the early evolution, the basin had a high geothermal gradient, lower rate as the deposition becomes larger; late geothermal gradient value is smaller. The historical geothermal gradient is above the present geothermal gradient; apparently higher Paleo-geothermal gradient is in favor of organic matter evolution and maturation heat required for the formation of hydrocarbons. However, during basin uplift and erosion, all faulted paleomagnetic temperature gradient increased.
In the transverse direction, the geothermal gradient at different times, in different tectonic evolution of the basin with their relative value is compared. Bo-Tai sag (
On the basis of accurate restoration of the thermal history, the chemical kinetics of the LLNL-Easy% Ro model was employed to recover mature evolution of hydrocarbons (
1) Bo-Tai sag (Well Chang 8): Eocene Shuangyang (E2s) source rocks in the early Eocene sedimentary Yongji formation about 38 Ma entered the hydrocarbon threshold (Ro = 0.5%) (
Well | Chang 7 | Chang 8 | WC 1 | Chang 25 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Depth (m) | 7 | 2820 | 3427.6 | 3755.1 | 3813.6 | 2402.5 | 2836.5 | 3485.5 | 3505 | 3796.5 | 3882.3 | 4131.3 |
Geothermal (˚C) | 94.44 | 105.5 | 133.89 | 145.6 | 147.22 | 90 | 106.7 | 132.2 | 131.11 | 147.22 | 149 | 151.11 |
about 36 Ma entered into the hydrocarbon threshold; Oligocene sedimentary Wanchang about 27 Ma entering the final stages of a large quantities of oil generation, Eocene Yongji formation (E2y) source rocks in the sedimentary entered the hydrocarbon threshold in the early Oligocene about 31 Ma; Neogene Chaluhe strata in the upper sedimentary approximately 15 Ma is also at its oil generation stage and is still at this stage, while the lower strata is not into oil generation but still in biogenic gas phase.
2) Xinanpu sag of the Chaluhe basin (Well Chang 25): Eocene Shuangyang (E2s) source rocks in the Eocene Yongji formation early deposition about 40 Ma entered the hydrocarbon threshold (
3) Wanchang structural belt (Well WC 1): Eocene Shuangyang (E2s) source rocks and the early Eocene Yongji sedimentary formation about 38 Ma entered the hydrocarbon threshold (
In summary, the Eocene formation source rocks in the Bo-Tai sag (Wells Chang 7 and Chang 8) has varying degrees of thermal evolution in different regions. Eocene Shuangyang and Sheling source rocks presently have reached a mature stage of oil production and above (Ro > 0.7%). Eocene overlying Yongji formation source rocks has entered a mature hydrocarbon threshold; Xinanpu sag’s (Well Chang 25) lower Eocene Shuangyang source rocks have reached the present gas generation phase, Shuangyang upper and lower part Sheling source rocks are into the mature stage of oil generation, and a lot of upper Sheling and Yongji formation source rocks have reached middle mature stage.
The summary of results interpretation and findings as discussed above of the one Dimensional (1D) Oil and Gas Generated/Expelled is undertaken for all four wells: Chang 7, 8, 25 and WC 1. The main focus as per the objectives set out in this study would do a summary of formations that contain the main hydrocarbon kitchen.
As per
Well No. | Chang 7 | Chang 8 | WC1 | Chang 25 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Horizons | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y |
Goil (mg/g TOC) | 27.39 | 14.7 | 5.03 | 35.85 | 29.8 | 11.39 | 22.69 | 10.02 | 3.15 | 39.49 | 27.05 | 14.92 |
Gtime (Ma) | 36.11 | 31.66 | 26.35 | 38.07 | 35.61 | 28.2 | 34.87 | 30.42 | 26.2 | 41.4 | 32.15 | 28.69 |
Deducting from
Presently, there is no Oil expelled from the Eocene Yongji formation source units into traps of reservoirs of all the four Wells considered in this study. The Shuangyang formation has the highest Oil expelled from all Wells under the study area with Well Chang 8 been the highest followed by Wells Chang 25, 7 and WC 1 in that order as per the
Well Chang 25 Lower Eocene Shuangyang formation in the Xinanpu sag within the Chaluhe basin which remains the main and only source unit presently records the highest expulsion of 72 mg/g TOC followed by Well Chang 8, 7 and WC 1 source units 64.26 mg/g TOC, 46.17 mg/g TOC and 22.02 mg/g TOC respectively as per
Wells maturity data showed that most or the entire source rocks buried below 2000 m within all the seismic regions analyzed in this study are matured.
Fortunately, all of the oil generated in these wells is expelled into the silty mudstone dominated reservoirs in the Eocene Shuangyang formation but Gas was not generated and expelled from some of the source units in the study area of some of the wells. This may not be the situation entirely within the whole study area since prevalent geological conditions may differ slightly from place to place.
Finally, it is recommended that, source units with high generation and expulsion rates and quantities could have their reservoirs exploited for these hydrocarbons by drilling of wells in these reservoirs.
Well No. | Chang 7 | Chang 8 | WC1 | Chang 25 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Horizons | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y |
Ggas (mg/g TOC) | 61.22 | 31.73 | 11.68 | 80.25 | 65.75 | 25.88 | 50.48 | 22.96 | 6.98 | 92.83 | 60.43 | 32.93 |
Gtime (Ma) | 36.11 | 31.66 | 26.35 | 38.07 | 35.61 | 28.2 | 34.87 | 30.42 | 26.2 | 41.4 | 32.15 | 28.69 |
Well No. | Chang 7 | Chang 8 | WC1 | Chang 25 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Horizons | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y |
Eoil (mg/g TOC) | 20.94 | 5.08 | - | 28.31 | 21.79 | - | 10.04 | - | - | 25 | 16.55 | - |
Etime (Ma) | 20.5 | 10.5 | - | 27 | 20.5 | - | 14.5 | - | - | 24.5 | 18 | - |
Well No. | Chang 7 | Chang 8 | WC1 | Chang 25 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Horizons | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y | E2s | E2sh | E2y |
Egas (mg/g TOC) | 46.17 | 10.67 | - | 64.26 | 48.05 | - | 22.02 | - | - | 72.16 | 36.15 | - |
Etime (Ma) | 20.5 | 10.5 | - | 27 | 20.5 | - | 14.5 | - | - | 24.5 | 18 | - |
The Authors are grateful to the Department of Oil and Gas exploration, Faculty of Earth Resources, China University of Geosciences (Wuhan) for their support in terms of data and finance.
Obed Kweku Agbadze,Jiaren Ye,Qiang Cao, (2016) One Dimensional Evolution Modeling of Source Rocks in the Chaluhe Basin, Yitong Graben. International Journal of Geosciences,07,1029-1048. doi: 10.4236/ijg.2016.78078