4D gravity response of compacting reservoirs: Analytical approach

Abstract

Time-lapse gravity is a technique sensitive to subsurface change in mass and in mass distribution. We attempted to devise a method to predict gravity effects caused by redistribution of subsurface mass induced by reservoir compaction. First, displacements and strains due to compaction were modeled using a geomechanical model. Then, 4D gravity effects were derived from the displacements and the volumetric strains computed in and around the reservoir. A sensitivity study was carried out for geomechanical parameters, such as Poisson’s ratio, as well as for geometrical parameters, such as reservoir radius and depth. Finally, changes in gravity due to compaction were compared to changes induced by reservoir fluid substitution. Given a rigid basement close below a strongly compacting reservoir, our modeling case showed that the deformation itself could give gravity changes comparable to changes caused by reservoir fluid density changes, which are the changes traditionally targeted by gravity monitoring. For a homogeneous subsurface, the compaction gave negligible gravity changes for our modeling case.

Study on the Macro-Fine Mechanical Behavior of Ore Flow Based on the Discrete Element Method

“…This phenomenon reflects that the contact strength between ore-rock particles is obviously affected by the ore-rock's gravity compaction. The effect of gravity compaction, based on the study results of Tempone, P., et al [40], is mainly manifested in that it changes the contact mode between irregular ore-rock particles and reduces the voidage of the particle system.…”

Intelligent element: Coupling Green function approach and artificial intelligence to reduce discretization effort

“…Between each neuron layer, a batch normalization layer was used to increase the stability of the element. 69 This layer has the function of normalizing the output of the previous layer according to the Equations ( 8), (9), and (10), in which 𝜖 is a constant add for numerical stability:…”

“…Some of the main changes caused due to pore pressure variation that deserve attention are the compaction of the reservoir, which affects the permeability of the rock, reducing the fluid extraction rate 1–3 and, possibly, closing the well 4,5 ; the subsidence or lifting of the free surface which can affect the functionality and stability of structures present in the region 6 . In addition, the monitoring of the massif behavior during the production of hydrocarbons is done through seismic measurements, 7–10 which relate to the variation of the strain field and to the variation of pore pressure in the reservoir to make predictions regarding the state of the massive.…”

3D Displacement and Stress Fields of Compacting Reservoir: Alternative Solutions

“…The main drawbacks in Geertsma and van Opstal (1973) and Tempone et al (2010) are the assumption of a homogeneous reservoir and the fact that the solution is only valid outside the reservoir. In this case, the displacements within the reservoir are calculated by linear interpolation of the displacements at the upper and lower edges of the reservoir Tempone et al (2012). Considering an inhomogeneous poroelastic model that consists of layered stratigraphy, Mehrabian and Abousleiman (2015) developed closed-form formulae for the displacement and stress fields outside and inside of the reservoir embedded within elastic strata with different mechanical properties and subjected to pore pressure disturbances due to fluid extraction or injection.…”