On the collapse behaviour of oil reservoir chalk

Suction and time effects on the behaviour of a reservoir chalk

“…The figure shows that there is obviously little effect of the pore fluid(s) in the elastic regime whereas differences appear in terms of yield stress and plastic compression. In the plastic regime, the stress-strain curves are correctly ordered as a function of both pore fluid and suction value, as already observed in oedometer compression results by De Gennaro et al (2004). However, some effects of the initial porosity on the sample stiffness in the plastic regimes appear to be also considered.The stiffest response obtained with the dry sample (n = 41.1%) has been commonly observed by various researchers (Masson 1973, Bonvallet 1979.…”

A model for pore‐fluid‐sensitive rock behavior using a weathering state parameter

“…Homand and Shao [20] and Collin et al [23] reported from a comprehensive suite of tests that the strength of oil-saturated Lixhe chalk is greater than that of water-saturated chalk ( Figure 1). These findings were confirmed and extended consistently to the intermediate state of partial saturation with oil and water during the PASACHALK project [24,27,29] where a series of hydrostatic, triaxial, and oedometric compression tests were performed under controlled partial saturation in oil and water. Talesnick et al [22] and Talesnick and Shehadeh [35] reported that uniaxial compressive strength and radial compressive strength of partially saturated solid and hollow cylinders of Marasha chalk (from Israel) vary smoothly with water saturation.…”

“…The physical mechanism of capillarity has also been proposed as the water-weakening mechanism for chalks containing two immiscible pore fluids [29]. Capillarity is part of the pore fluid total potential also called total suction in soil mechanics.…”

“…The basis for the capillary mechanism is that under conditions of low water saturation, the water menisci bind more tightly to the preferentially water-wet solids at lower water saturation. This physical action stands together with the chemical interactions between the pore fluid and the solid skeleton (adsorption and electrostatic interactions), the extent of which will depend on the nature of both fluid and solid material (see References [26,29]). If one accounts only for the physicomechanical interaction associated with capillary pressure (see also [41]) this will cause the effective inter-granular stress to increase as water saturation decreases, which in turn increases the apparent cohesion or intergranular attraction in the chalk.…”

“…An appealing characteristic of the BBM is that it provides a sound description of the pore collapse phenomenon that occurs in partially saturated soils or porous rocks when wetted under load. The collapse strain is a plastic phenomenon that follows the yield curve called the loading-collapse curve [29]. Total suction includes the effects of capillarity together with other possible physico-chemical solid-fluid interactions that may occur in the chalk [24,27,29,31].…”