CN-115980879-B - Method for identifying coexistence of hydrate and free gas in block carrying and depositing development area

Abstract

The invention discloses a method for identifying the coexistence of hydrate and free gas in a block transportation sediment development zone, which is characterized in that the influence of new sediment effect on the thickness of a hydrate stability zone is analyzed to judge various contact relations between hydrate and free gas in the block transportation sediment development zone, and the research contents such as abnormal change identification of logging, geological and sediment condition analysis, seismic wave impedance inversion, hydrate stability zone thickness adjustment calculation, BSR identification and formation lithology identification of a hydrate coexistence layer in the block transportation sediment development zone are utilized to realize the rapid identification of hydrate and free gas coexistence layer in the block transportation sediment development zone, so that the understanding of the biogenic gas as a main air source and a dynamic formation system of hydrate in the rapid sediment development zone is obtained, the coexistence of hydrate and free gas in the block transportation sediment zone is innovatively explained, the spatial distribution of hydrate and free gas in the rapid sediment zone can be reasonably explained, and basis is provided for the subsequent exploration and development of hydrate reservoirs.

Inventors

• WANG XIUJUAN
• LIU HUAISHAN
• LIU BO
• LI SANZHONG
• HU GAOWEI
• XING LEI
• JIN JIAPENG
• YAN WEICHAO
• ZHANG GUANGXU
• ZHANG ZHENGYI

Assignees

• 中国海洋大学
• 河北工程大学

Dates

Publication Date

20260505

Application Date

20221229

Claims (3)

1. 1. A method of identifying the coexistence of hydrate and free gas in a bulk handling deposition development area comprising the steps of: Step A, identifying hydrate and a free gas layer: A1, calculating a hydrate stability zone bottom boundary based on logging data, calculating saturated water longitudinal wave speed and saturated water resistivity, and identifying a hydrate layer and a free gas layer; A2, synthesizing an earthquake record based on logging data and earthquake data, establishing a time-depth relation between logging and earthquake, performing constraint sparse pulse wave impedance inversion to obtain wave impedance data, and comparing the wave impedance data with the logging data to define a hydrate and a free gas layer by using the wave impedance data; And B, analyzing BSR changes affected by rapid deposition: Step B1, identifying the spatial distribution range of a block carrying and depositing layer according to seismic data and geological knowledge of a target area, and determining the thickness of the block carrying and depositing layer by combining logging data; step B2, judging BSR standards by utilizing the seismic data and geological knowledge of the target area, and identifying all BSR reflections in the whole research range, analyzing the seismic amplitude intensity change among a plurality of BSR reflections, and converting the time between BSRs into thickness by utilizing the time-depth relation of synthetic seismic records; and B3, analyzing the thickness of the stratum newly deposited on the seabed in the corresponding deposition time based on geological data of the core region, wherein after the stratum is newly deposited, the temperature change of the stratum is a function of the depth z and the time t, and is expressed as: , wherein G is the ground temperature gradient, v is the formation erosion rate or deposition rate, For the thermal conductivity of the formation, , And Initial subsea temperature and depth, respectively, formation thermal conductivity Calculating the thickness change of the hydrate stability zone bottom boundary along with the deposition by utilizing the hydrate phase equilibrium curve and the combination of the above-mentioned method; step B4, based on the step B1 and the step B2, combining the depth of upward adjustment of the bottom boundary of the stable band calculated in the step B3, interactively verifying and explaining the thickness change of the BSR or the hydrate stable band caused by rapid block handling deposition; And C, analyzing the contact relation between the BSR of the block carrying and depositing development zone and the hydrate and the free gas by combining the hydrate and the free gas layer identified in the step A and the BSR change which is analyzed in the step B and is influenced by the rapid deposition, so as to identify the coexistence zone of the hydrate and the free gas of the block carrying and depositing development zone.
2. 2. The method for identifying the coexistence of hydrate and free gas in a mass transfer and deposition development area according to claim 1, wherein in the step A2, the measured resistivity and longitudinal wave velocity are compared with the saturated water resistivity and saturated water longitudinal wave velocity calculated in the step A1, and the calculated hydrate stability zone bottom boundary is combined, and the stratum is considered to contain hydrate if the measured result is larger than the calculated background trend, and otherwise, the stratum is considered to contain free gas.
3. 3. The method for identifying the coexistence of hydrate and free gas in a mass handling sediment development zone according to claim 1, wherein in the step C, the new BSR is an interface between the hydrate and the coexistence layer of the hydrate and the free gas, the original BSR is an interface between the hydrate and the coexistence layer of the free gas, and the new BSR and the original BSR belong to the coexistence region of the hydrate and the free gas.

Description

Method for identifying coexistence of hydrate and free gas in block carrying and depositing development area Technical Field The invention belongs to the field of petroleum and natural gas hydrate exploration, and particularly relates to a rapid discrimination method for coexistence of a sand reservoir hydrate and free gas in a block carrying and depositing development area. Background The hydrate is a compound similar to ice solid, exists in a low-temperature and high-pressure environment, is influenced by gas components, salinity and the like, and is mainly classified into type I, type II and type H hydrates in nature. Under static conditions, hydrate occurrence depths are affected by the warm-pressure conditions, and a seafloor-like reflection (BSR) is formed on the seismic profile, but a plurality of BSRs or double BSRs exist in many areas. At present, double BSR or multiple BSR are found in various sea areas internationally, and the formation reasons of the double BSR or the multiple BSR are various factors such as rapid deposition of the seabed, erosion of the submarine canyon or the submarine landslide, elevation of the sea level, temperature change of the seabed, influence of construction activities and the like. Different factors lead to the upward movement or downward movement of the BSR, the gas source for forming the hydrate can be biogenic gas or thermogenic gas, the reservoir conditions can be fine-grained argillite sediment or sandy reservoir, and the condition that natural gas hydrate and free gas coexist in the upper and lower regulating areas of the stabilizing zone can occur in the regulating process of the new equilibrium state which is not achieved due to the time required for BSR regulation. The block carrying sediment is widely developed in a deep basin and mainly comprises three structural units, namely a head stretching area, a body sliding area and a toe extrusion area, the seismic characteristics and logging anomalies of different structural units are different, and the sediment rate is far higher than that of a normal sediment stratum due to the rapid accumulation of the block carrying sediment, so that the rapid change of submarine temperature and pressure conditions is caused, the thickness of a hydrate stabilizing zone is influenced, and therefore, the formation and decomposition of the hydrate are considered to be closely related to the block carrying sediment or a submarine landslide, and the direct evidence about the relationship between the formation and decomposition is less due to the limitation of drilling data. In the formation of block transportation sediment, abnormal such as amplitude blank, weak amplitude reflection and the like can occur on the seismic section, the hydrate is mostly developed in the lower turbid deposit or normal sediment formation of the block transportation sediment, the hydrate is not developed in the block transportation sediment, and the early research is mostly focused on the formation mechanism, distribution and influence of the formation mechanism, the distribution and the hydrate on the identification and the accumulation of the block transportation sediment. The seismic response characteristics of the bulk carrying sedimentary formations are characterized by discontinuous, blank-disordered, low-amplitude or transparent reflection characteristics on the seismic section, the physical properties of internal sediments are not changed greatly, but the density and the sound wave speed of the internal sediments are increased compared with those of surrounding adjacent formations, so that the relative wave impedance of the internal sediments is higher than that of surrounding rocks, the internal sediments have obvious top-bottom interfaces, the top interfaces are the propagation of sound waves from low-impedance formations to high-impedance formations, positive-polarity strong-amplitude reflection consistent with the polarity of the seabed is formed, the bottom interfaces are the propagation of sound waves from high-impedance formations to low-impedance formations, negative-polarity reflection opposite to the polarity of the seabed is formed, the bottom interfaces are often in erosion properties, and scratches can be identified on the plane characteristics. Due to the dehydration, extrusion and other actions of the block transportation sedimentary strata during the transportation process, a backflushing fault can be formed at a local position, and the stratum permeability is reduced. Thus, bulk handling depositional development zone hydrate formations are more complex and have complexity and heterogeneity with spatial spread compared to normal depositional formations. From logging while drilling data at different sites of new zealand, the bottom of the stratum where the bulk carrying sediment is contained at different well sites, the longitudinal wave velocity and the resistivity are slightly increased, but the density is also increased, from pr