Rich argillaceous sand stone three-dimension equivalent speed prediction model

Abstract

The invention relates to a rich argillaceous sand stone three-dimension equivalent speed prediction model which is deduced by improving a method of calculating elastic modulus of dry rocks in a Xu-White speed prediction model. The model calculates the elastic modulus of dry rocks by replacing the aspect ratio of a fixed pore in the Xu-White model by four three-dimension shape (spherical shape, needle shape, tray shape and crack shape) pores which are raised by Berryman (1955) according to a statistic pore distribution spectrum, the improved model can simulate the geometric size which is more close to argillaceous micro cracks in rich argillaceous sand stone by freely adjusting the pore aspect ratio, thereby directly and truly reflecting the shape of underground reservoir space and ensuring the coincidence of a predicted result and the actual measuring result.

Description

technical field [0001] The invention relates to a velocity prediction model suitable for argillaceous sandstone, especially argillaceous sandstone reservoirs, which considers the influence of three-dimensional pore space structure of rocks, and belongs to the technical field of rock physics. Background technique [0002] In addition to being affected by properties such as porosity and saturation, the seismic wave velocity is also obviously affected by the pore space structure, that is, the pore shape. This is an indisputable fact. Many scholars have done a lot of research on this, such as Kuster with (1976), Sun et al (1991, 2004), Anselmetti and Eberli (1993, 1999), Wang (2001), Yan et al (2002), Zhang and Bentley (2003), Baechle et al (2008), Wang et al (2009 ). In the velocity prediction model of clastic reservoirs, the Gassmann equation (1951), Model (1974) and Xu-White model (1995) are the three main rock physical velocity prediction models. However, these three ...

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Problems solved by technology

However, these three models have certain limitations in considering the influence of pore shape: Although the Gassmann equation considers the isotropy of the pore, it does not take into account the change of the pore shape and assumes that it is spherical; On the premise that the pore shape is assumed to be an ellipsoid, the model takes pores of various sizes into the model calculation by introducing a two-dimensional pore-surface ratio that can be adjusted arbitrarily, but as a very high-frequency model, the pores in the rock are required to be sparse and isolated, which limits the interaction between the pores and the fluids within the pores; the Xu-White model is designed to be able to resemble Like the shaly sandstone, the model can also consider the influence of pore shape on the seismic wave velocity. It divides the rock pores into sandstone pores with a large pore-to-surface ratio (about 0.12) and mudstone pores with a small pore-to-surface ratio (about 0.02-0.05). For general sandstone reservoirs with less shale, since the pore space is dominated by sandstone pores with a large pore-to-surface ratio, although the method of fixing the pore-to-surface ratio of the mudstone in the Xu-White model does not conform to the actual geometric size of the mudstone pores, but due to The total amount is small, and it can still meet the needs of considering the influence of rock average pore geometry size on seismic wave velocity

However, for shale-rich sandstone reservoirs, due to the high shale content, the influence of micro-cracks developed in the shale on the seismic wave velocity is highlighted. At this time, the Xu-White model's method of fixing the pore-to-surface ratio of the mudstone is no longer satisfactory. needed

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