Prediction of Reservoir Compaction and Surface Subsidence: Field Application of a New Model

Abstract

A new loading-rate-dependent compaction model for unconsolidated clastic reservoirs is presented that considerably improves the accuracy of predicting reservoir rock compaction and surface subsidence resulting from pressure depletion in oil and gas fields. The model has been developed on the basis of extensive laboratory studies and can be derived from a theory relating compaction to time-dependent intergranular friction.The procedure for calculating reservoir compaction from laboratory measurements with the new model is outlined. Both field and laboratory compaction behaviors appear to be described by one single normalized, nonlinear compaction curve. With the new model, the large discrepancies usually observed between predictions based on linear compaction models and actual (nonlinear) field behavior can be explained .

Subsidence Delay: Field Observations and Analysis

“…This phenomenon has been observed before (Merle et al, 1976;de Waal and Smits, 1985;Boutéca et al, 1990;McLendon, 1991). Unfortunately, only a few subsidence fields have reliable early measurements available.…”

“…It is possible that a "geologically instantaneous" increase in loading rate of several orders of magnitude is accompanied by a time delay effect. De Waal and Smits (1985) have developed a mathematical model to relate the compaction to both the geological and the depletion-induced loading rates. The key to understanding loading rate effects lies in the analysis of the grain scale micro-mechanism, and more specifically, to the relationship between local thermodynamic driving force and kinetics of the grain-scale deformation mechanism(s) like stresscorrosion cracking (Atkinson, 1987) or pressure solution (Lehner, 1995).…”

Creep of Posidonia Shale at Elevated Pressure and Temperature

“…Creep experiments on shales focus on compaction and consolidation (Cogan, 1976;de Waal and Smits, 1988;Dudley et al, 1998), the effect of adsorption and swelling on creep (Heller and Zoback, 2011;Hol and Zoback, 2013) and on viscoelastic or viscoplastic creep of shales in response to nanoindentation (Mighani et al, 2015) and applied differential stresses at elevated confining pressures (Almasoodi et al, 2014;Zoback, 2009, 2010;Chong et al, p [5] creep is enhanced at high differential stress, high clay content, in the presence of water and if loaded normal to bedding orientation. For the examined North American shales the influence of confining pressure appears to be either absent or reducing creep rates only slightly up to a few tens MPa confinement.…”

Unraveling reservoir compaction parameters through the inversion of surface subsidence observations

“…This nonlinearity in subsidence response may be seen as a shift between the start of depletion and the (delayed) start of subsidence [19], or as an increase in subsidence rate with time. This time lag in subsidence response has been observed for several oil and gas fields (e.g., Bachaquero [19][20][21], Tia Juana [19,22], the SNOK field [23], and Wilmington [21,24]). The underlying cause of the time lag has been attributed to mechanisms related to reservoir compaction (such as creep, an intrinsic rate effect, and an elastic-plastic transition, [19]).…”

“…Alternatively, the nonlinearity of the subsidence response is attributable to the compaction coefficient being dependent on depletion: hence, the gradual response in reservoir compaction. De Waal and Smits [21] have developed a model on the basis of extensive laboratory studies. The model was derived from a theory relating compaction to time-dependent intergranular friction and explains both field and laboratory compaction behavior by one single normalized, nonlinear compaction curve.…”