CN117031545B - Method for identifying hydrate and free gas coexistence layer of sandy reservoir based on sensitive parameters - Google Patents
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Abstract
The invention provides a sensitive parameter method for identifying a sand reservoir hydrate and free gas coexistence layer, which is used for calculating actual stratum elasticity parameters lambda rho, mu rho and lambda/mu based on measured density, longitudinal wave speed and transverse wave speed logging data, deducing saturated water sand reservoir elasticity parameters lambda/. Mu and mu rho theoretical values according to a rock physical speed model, establishing a lambda/. Mu-Vp and mu rho-Vp intersection model for dividing the sand reservoir hydrate layer, the free gas layer, a saturated water layer and the hydrate and free gas coexistence layer by analyzing and comparing the changes of physical properties of different rock stratum reservoirs, and effectively identifying and predicting the sand hydrate and free gas coexistence reservoir by different areas Vp, lambda/. Mu and mu rho and background trend relations.
Description
Technical Field
The invention belongs to the field of hydrate test production reservoir evaluation, and particularly relates to a method for identifying a sandy reservoir hydrate and free gas coexisting layer based on sensitive parameters.
Background
The hydrate saturation in the sandy reservoir is up to 80% as found by a large amount of hydrate drilling, and the sandy reservoir hydrate and free gas coexist and widely develop due to the influence of various factors such as rapid deposition, structure Long Sheng, overpressure, thermal forming gas and the like, and not only the hydrate with high saturation but also a hydrate and free gas coexistence layer (coexistence layer for short) is found in sandy reservoirs such as the east coast of india, the southwest basin of south-sea-agar in China, the netherlands of new zealand, the brown-in diving zone and the like, but the free gas layer may develop in the lower part of the coexistence layer.
From logging data, the logging response characteristics of the coexisting layer are similar to those of the lower free gas layer, the water-containing compound layer has high longitudinal wave speed and high transverse wave speed, the longitudinal wave speed of the free gas layer is reduced and the transverse wave speed of the free gas layer is not changed obviously, the coexisting layer has low longitudinal wave speed similar to that of the free gas, but the transverse wave speed is changed greatly, and if the coexisting layer is mainly hydrated, the transverse wave speed is abnormal at a high value. It was found that if the coexisting layer is interpreted as a free gas layer, the free gas saturation calculated using the longitudinal wave velocity is about 1-2% assuming a uniform distribution of the free gas, but if the low velocity anomaly is caused by the coexistence of hydrate and free gas, the sum of the calculated two saturations is 30-40%, and therefore, such erroneous interpretation will underestimate the amounts of resources of hydrate and free gas which are contained in the coexisting layer, resulting in a severely lower estimated amount of resources.
Sand reservoirs will also be an advantageous target for future commercial development of hydrates if present with free gas. Therefore, the research on the coexistence of hydrate and free gas in the development area of the sandy reservoir, especially the highly enriched sandy reservoir, has important significance for finding out the hydrate reservoir system and the hydrate test exploitation target thereof. At present, from logging data, logging response of the coexisting layer is similar to that of the free gas in the stratum, low longitudinal wave velocity anomalies are shown, and in seismic exploration, how to distinguish the coexisting layer from the free gas layer has important significance for accurately estimating the resource quantity of a sandy reservoir and searching for a hydrate test production providing target.
In the prior art, a great deal of land and deep consolidated formation sandy reservoir hydrocarbon gas identification and sensitive attribute research is carried out by the former, such as LMR (Lambda-mu-rho ) intersection analysis, and the identification of sandy reservoir hydrocarbon gas is carried out by intersection analysis through the combination of the plum pulling parameters and the density (Lambda rho and rho). However, ocean hydrates are located in formations within 300m of the ocean floor and are unconsolidated formations, and reservoir parameter changes of the coexisting formations are related to formation hydrate content, and it is difficult to directly identify the coexisting formations using LMR intersection analysis, mainly in two aspects: first, the low density, low saturation hydrate layer is not easily distinguishable from saturated water formations and gas bearing formations; second, the free gas layer and the coexisting layer are both abnormal in low longitudinal wave velocity, and conventional oil gas sensitive parameters are not easy to distinguish between the free gas layer and the coexisting layer. Thus, the partitioning method in conventional hydrocarbon exploration would consider the coexisting layers as gas bearing layers, thereby affecting accurate assessment of the hydrate reservoir system and its resource amount.
Therefore, how to determine sensitive parameters of the hydrate and free gas coexisting layers of the sandy reservoir based on the petrophysical model by means of logging data, finely identify and divide the lithofacies of the coexisting layers, predict the high-enrichment favorable target and solve the problems of further hydrate trial production and realizing commercial exploitation.
Disclosure of Invention
The invention provides a method for identifying a sandy reservoir hydrate and a free gas coexisting layer based on sensitive parameters, which aims to solve the defect that the hydrate and the free gas coexisting layer are difficult to directly identify by utilizing LMR intersection analysis in the prior art, and the coexisting layer is identified by utilizing the difference of lambda/mu and mu rho parameters of the free gas layer and the coexisting layer, so that the method is favorable for identifying and predicting the coexisting target of the sandy reservoir highly enriched hydrate and the free gas by combining the high longitudinal wave velocity characteristic of the high-saturation hydrate layer.
The invention is realized by adopting the following technical scheme: the invention provides a method for identifying a sandy reservoir hydrate and free gas coexisting layer based on sensitive parameters, which comprises the following steps:
firstly, calculating the background values of resistivity, longitudinal wave and transverse wave speeds of a saturated water sand reservoir, comparing and analyzing logging measured data with the calculated background values of the saturated water sand reservoir, and identifying lithofacies such as a saturated water layer, a hydrate layer, a free gas layer, a coexisting layer and the like by combining core analysis results and neutron porosity and density porosity differences;
secondly, deducing actual stratum elastic parameters lambdaρ, μρ and lambdaμ by using the density, longitudinal wave speed and transverse wave speed logging values, and carrying out intersection analysis of various parameters including LMR (lambdaρ - μρ), lambdaλ/μ -Vp and μρ -Vp;
then based on a simplified three-phase medium model, the compaction coefficient is selected to be about 30-100, the formation lithology is 70% sand+30% mud, theoretical values of sensitive parameters lambda/mu and mu rho of saturated water sand reservoirs with different porosities and different depths are calculated, the porosities are selected to be 60%, 65% and 70%, the depths are selected to be 200m, 300m and 400m, and a background trend of a cross map of the saturated water sand reservoirs lambda/mu-Vp and mu rho-Vp is established;
and finally, analyzing the distribution characteristics of the actual logging data sample points deviating from the background trend by combining the analysis results of various parameter intersections and the background trend, and identifying the hydrate and free gas coexistence layer according to the characteristics of the low Vp, the low lambda/mu and the low Vp and the high mu rho trend.
Compared with the prior art, the invention has the advantages and positive effects that:
according to the scheme, the sensitive parameters lambda/mu and mu rho of the hydrate and free gas coexistence layer are determined, longitudinal wave speed and transverse wave speed differences of the hydrate, the free gas and the coexistence layer and a saturated water stratum are fully utilized, and different lithofacies of the sandy reservoir are divided through intersection analysis of the sensitive parameters (lambda/mu-Vp and mu rho-Vp) so as to effectively identify and predict the sandy reservoir characteristics.
Drawings
FIG. 1 is a flow chart of determining sensitive parameters of a sand hydrate and free gas coexistence layer according to an embodiment of the present invention;
FIG. 2 is a schematic view of an embodiment of the present invention for interpreting different lithofacies of a sandy reservoir using log data;
FIG. 3 is a schematic diagram of LMR intersection analysis;
FIG. 4 is a schematic diagram illustrating analysis of the interaction of sensitive parameters μρ -Vp of the coexisting layers according to an embodiment of the present invention;
FIG. 5 is a schematic diagram illustrating analysis of the co-existence layer sensitivity parameter lambda/. Mu. -Vp intersection in accordance with an embodiment of the present invention.
Detailed Description
In order that the above objects, features and advantages of the invention will be more readily understood, a further description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced otherwise than as described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.
The conventional lithofacies classification method of oil and gas can accurately identify and classify the oil and gas-containing stratum by establishing sensitive parameters (lambada rho and rho) intersection analysis (namely LMR intersection analysis) related to the parameter of the plum pulling according to the low density and low longitudinal wave speed characteristics of the oil and gas-containing stratum. However, for a high porosity sandy reservoir, a hydrate layer with low saturation and slightly low density is not easily distinguished from a saturated water stratum, and a free gas layer and a coexisting layer are both abnormal in low longitudinal wave velocity and are not easily distinguished, so that conventional oil and gas sensitive parameters are difficult to effectively identify the hydrate layer and the coexisting layer.
The embodiment provides a method for identifying a sandy reservoir hydrate and free gas coexistence layer based on sensitive parameters, which is based on measured sandy reservoir density (ρ), longitudinal wave velocity (Vp) and transverse wave velocity (Vs) logging data, deduces elastic parameters of an actual reservoir, namely λρ, μρ and λ/μ, carries out intersection analysis of various parameters including LMR (λρ - μρ), λ/μ -Vp and μρ -Vp, combines a petrophysical velocity model, analyzes and calculates theoretical values of the sensitive parameters of the saturated water and sand reservoirs, namely λ/μ and μρ, of different porosities and different depths, establishes background trends of a saturated water and sand reservoir, namely λ/μ -Vp and μρ -intersection map, and effectively identifies and predicts the sandy hydrate and free gas coexistence reservoir by combining relations between different areas, namely Vp, λ/μ and μρ and background trends, and specifically comprises the following steps:
step A: interpreting different lithofacies of the sandy reservoir based on the logging data;
the resistivity, longitudinal wave velocity and transverse wave velocity theoretical values of the saturated water stratum are calculated by using the density logging data based on Archie (1942) and a simplified three-phase medium model (Lee, 2008), compared with the measured logging values, and different lithofacies such as hydrate, free gas and coexisting layers are identified by combining the density porosity and neutron porosity difference.
As shown in fig. 2, wherein (1) the 291-295m depth exhibits high resistivity, high longitudinal wave velocity and high transverse wave velocity log responses, indicative of formation hydrate; (2) The depth of 295-306m exhibits a high resistivity, low compressional velocity, and neutron porosity lower than the density porosity log response, indicating that the formation contains free gas, but at the depth of 295-297m, a high resistivity, high shear velocity, high and low compressional velocity log response occurs, which is different from the free gas containing log response, considered as a hydrate and free gas coexistence layer; (3) At a depth of 297-306m, the formation exhibits high resistivity, low compressional velocity, and no significant change in shear velocity, indicating that the formation contains free gas. The measured values of the resistivity, the longitudinal wave velocity and the transverse wave velocity are compared with the calculated background value of the saturated water stratum, and the water-containing compound layer is abnormal in high resistivity, high longitudinal wave velocity and high transverse wave velocity; the free gas layer has high resistivity, low longitudinal wave speed abnormality and no obvious change of transverse wave speed, and the coexisting layer has high resistivity, low longitudinal wave speed and high transverse wave speed; neutron porosity is lower than density porosity in both the free gas layer and the coexisting layer.
And B, calculating actual stratum elastic parameters lambdap, muρ and lambdap according to the sand reservoir density, the longitudinal wave velocity and the transverse wave velocity logging values, establishing a background trend of a lambda/mup-Vp and muρ -Vp intersection chart according to the calculated saturated water sand reservoir elastic parameters muρ and lambda/muρ theoretical values, analyzing the distribution difference of different lithofacies identified in the step A in the intersection chart by performing intersection analysis of LMR (lambda ρ -muρ), lambda/muvp and muρ -Vp parameters, and analyzing the sensitivity parameters lambda/muρ and trend characteristics of the hydrate and free gas coexistence layer by respectively and obviously distinguishing the three different lithofacies of the hydrate layer, the free gas layer and the hydrate and the free gas coexistence layer, wherein the three different lithofacies can be effectively identified by confirming the intersection chart, and the specific characteristics of the sensitive parameters lambda/mup and the trend of the hydrate and the free gas coexistence layer are determined:
(1) Deriving actual stratum elastic parameters lambdaρ, μρ and lambdaμ by using reservoir density, longitudinal wave velocity and transverse wave velocity log values, establishing a lambdaρ -lambdaρ intersection chart (fig. 3), and simultaneously establishing a lambdaμ/μ -Vp-muρ intersection chart (discrete points shown in fig. 4 and 5), wherein the elastic parameters are calculated as follows:
λρ＝(Vp·ρ) 2 -2(Vs·ρ) 2 (1)
μρ＝(Vs·ρ) 2 (2)
λ/μ＝(Vp/Vs) 2 -2 (3)
(2) Based on a simplified three-phase medium speed model (Lee, 2009), the compaction coefficient is selected to be about 30-100, the formation lithology is 70% sand+30% mud, theoretical values of density, longitudinal wave speed and transverse wave speed of sand reservoirs with different porosities (60%, 65%, 70%) and different depths (200 m, 300m, 400 m) are calculated, equation 1-3 is utilized to derive elastic parameters muρ and lambda/mu theoretical values of the saturated water sand reservoirs, and a background trend of a lambda/mu-Vp and muρ -Vp intersection graph is established (as shown by solid lines in fig. 4 and 5).
(3) Comparing the actual log data intersection relationship established in the step (1) with the background trend of the intersection map established in the step (2), and identifying the hydrate and free gas coexistence layer by the position deviated from the background trend (such as fig. 3, 4 and 5).
FIG. 3 is a conventional oil and gas sensitive parameter LMR (λρ - μρ) intersection analysis, and it can be seen from FIG. 3 that gas bearing formations (including free gas and coexisting layers) can be identified from the low λρ trend, but the parameter is not easily distinguishable from free gas and coexisting layers and is not easily distinguishable from hydrate layers. FIG. 4 shows that the intersection of the sensitive parameter μρ and Vp identifies the coexisting layer, and that the sensitive parameter intersection map is able to distinguish the hydrate layer from the gas bearing formation because the hydrate layer deviates significantly from the background trend due to the high longitudinal wave velocity characteristics and is located in a different direction from the background trend, respectively, compared to the conventional oil-gas LMR intersection analysis (FIG. 3). Although free airThe layer and the coexisting layer are both characterized by low longitudinal wave velocity and are positioned in the same direction of background trend, but the μρ value is more than 0.3GPa×g/cm because the coexisting layer is characterized by high transverse wave velocity 3 And the value of the μρ of the free gas-containing layer is less than 0.3GPa×g/cm 3 Therefore, the parameter μρ can distinguish the coexisting layer from the free gas-containing layer, and μρ -Vp can be used as a sensitive parameter intersection map for identifying the coexisting layer. FIG. 5 shows that the sensitive parameters lambda/. Mu.and Vp intersect to identify coexisting layers, similar to mu p-Vp intersection, the hydrate-containing layer and the gas-containing layer (including free gas and coexisting layers) can be divided according to longitudinal wave velocity difference, and the parameter lambda/. Mu.can distinguish the free gas-containing layer from the coexisting layers because the free gas-containing layer lambda/. Mu.value is greater than 13 and the coexisting layer lambda/. Mu.value is less than 13 due to transverse wave velocity difference, lambda/. Mu.can be used as a sensitive parameter intersection diagram for identifying coexisting layers.
And C, deducing elastic parameters muρ and lambda/mu according to the density, longitudinal wave speed and transverse wave speed logging data of the sandy reservoir to be identified, comparing the lambda/mu-Vp and muρ -Vp intersection model of the sandy reservoir hydrate layer, the free gas layer, the saturated water layer and the hydrate and free gas coexistence layer established in the step B by intersecting with the longitudinal wave speed Vp, and identifying and predicting the sandy reservoir hydrate and free gas coexistence layer according to low Vp, low lambda/mu and low Vp and high muρ trends.
And (3) deducing sensitive parameters muρ and lambda/mu by using the logging data of the density, the longitudinal wave speed and the transverse wave speed of the sandy reservoir to be identified through the equations (1) - (3) in the step B, respectively carrying out intersection analysis of muρ -Vp and lambda/mu-Vp, and comparing the position difference of a hydrate layer, a free gas layer, a saturated water layer and a coexisting layer in an intersection graph, wherein the free gas layer and the coexisting layer are in a low Vp deviation trend compared with a calculated background trend (solid lines in fig. 4 and 5) of the intersection graph, but the coexisting layer has a low lambda/mu and a high muρ deviation trend and is obviously different from the free gas layer. The free gas layer and the coexisting layer of the stratum can be accurately divided according to the method, so that the coexisting layer can be identified.
The sensitive parameters for identifying the coexistence of the hydrate and the free gas in the sandy reservoir based on intersection analysis provided by the invention are μρ and λ/μ, and the gas-containing layer (comprising the free gas layer and the coexistence layer) can be identified by intersection with the longitudinal wave velocity Vp, and the free gas-containing layer and the coexistence layer can be further and accurately divided. The method can provide technical support for rapid evaluation of subsequent hydrate reservoir exploration and development, and is favorable for rapid identification of target reservoir characteristics.
The present invention is not limited to the above-mentioned embodiments, and any equivalent embodiments which can be changed or modified by the technical content disclosed above can be applied to other fields, but any simple modification, equivalent changes and modification made to the above-mentioned embodiments according to the technical substance of the present invention without departing from the technical content of the present invention still belong to the protection scope of the technical solution of the present invention.
Claims (4)
1. A method for identifying a sandy reservoir hydrate and free gas coexistence layer based on sensitive parameters, comprising the steps of:
step A, interpreting different lithofacies of a sandy reservoir based on logging data;
b, calculating actual stratum elastic parameters lambada rho, murho and lambada/mu according to logging data, deducing elastic parameters murho and lambada/mu theoretical values of a saturated water sand reservoir according to a petrophysical velocity model, carrying out intersection analysis of lambada rho-murho, lambda/mu-Vp and murho-Vp parameters, analyzing distribution differences of different lithofacies identified in the step A in an intersection chart, and determining sensitive parameters lambda/mu and murho for identifying a hydrate and free gas coexistence layer;
and C, calculating elastic parameters murho and lambda/mu according to logging data of the sandy reservoir to be identified, and identifying the sandy reservoir hydrate and free gas coexistence layer according to trend characteristics of low Vp, low lambda/mu and low Vp and high murho by intersecting with the longitudinal wave velocity Vp and combining the analysis result of the step B.
2. The method for identifying a sand reservoir hydrate and free gas coexistence layer based on sensitive parameters according to claim 1, wherein: the step B specifically comprises the following steps:
step B1, calculating actual stratum elastic parameters lambdap, muρ and lambdap according to the sandy reservoir density, longitudinal wave velocity and transverse wave velocity logging values, and establishing a lambdap-muρ, lambdap-Vp and muρ -Vp intersection diagram;
step B2, calculating theoretical values of formation density, longitudinal wave speed and transverse wave speed of different porosities and different depths based on a simplified three-phase medium speed model, further deriving elastic parameters muρ and lambda/mu theoretical values of a saturated water sand reservoir, and establishing a background trend of a cross map of lambda/mu-Vp and muρ -Vp;
and B3, comparing the relation of the actual log data intersection diagram established in the step B1 with the background trend of the intersection diagram established in the step B2, identifying a hydrate and free gas coexisting layer by deviating from the position of the background trend, and analyzing and determining trend characteristics of the μρ, λ/μ for distinguishing the coexisting layer from the free gas stratum.
3. The method for identifying a sand reservoir hydrate and free gas coexistence layer based on sensitive parameters according to claim 1, wherein: in the step B, the elastic parameters lambdaρ, μρ and lambdaμ are calculated as follows:
λρ＝(Vp·ρ) 2 -2(Vs·ρ) 2
μρ＝(Vs·ρ) 2
λ/μ＝(Vp/Vs) 2 -2
where ρ is the formation density, vp is the longitudinal velocity, and Vs is the transverse velocity.
4. The method for identifying a sand reservoir hydrate and free gas coexistence layer based on sensitive parameters according to claim 1, wherein: in the step A, the theoretical values of resistivity, longitudinal wave speed and transverse wave speed of the saturated water sand reservoir are calculated, comparison analysis and logging interpretation are carried out on the theoretical values and logging measured data, and the rock phases of the saturated water layer, the hydrate layer, the free gas layer and the coexisting layer are identified by combining the core analysis result and the neutron porosity and density porosity difference.
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