Mineral Surface Chemistry in Critical Oilfield Operations

Christopher Hall Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL, UK


Much critical oilfield technology turns on the control of reactive flow in porous media. The paper discusses recent research on mineral surface chemistry related to new oilfield technology. Research needs and open questions are identified. Historically, reservoir engineering and geophysical measurement have been dominated by a petrophysical perspective. For many purposes, our knowledge of the chemical behaviour is inadequate. This is revealed by difficulties of modelling reactive flow in reservoir rocks.

Stimulation technology: acidising and acid fluids for water control

In matrix acidising, carbonate minerals (and clays) in reservoir rocks are deliberately dissolved to increase permeability. Dissolution patterns depend the relative magnitudes of chemical and convective terms. In water shut-off, calcite cements are probably dissolved as an unwanted side-effect during the placement of low pH gelling fluids. In both cases, lack of kinetic data and characterisation methods make prediction of dissolution uncertain. Solution composition
(eg buffer capacity) in convective flow schemes is discussed.

Scale formation and its inhibition

Precipitation of mineral scales (and severe permeability reduction) occurs when formation and injection waters mix. Crystal growth inhibitor "squeeze" treatments are widely applied. These depend on adsorption/desorption cycles and effective molecular design for inhibition. Radioactive scales (concentrating radium) pose environmental problems.

Cement chemistry under borehole conditions

Control of cement setting under deep borehole conditions (say 150°C) requires extreme chemical retardation of the hydration chemistry. Mechanisms are not well understood at the molecular level, although new techniques such as FTIR and synchrotron X-ray diffraction are slowly revealing facts about the early chemistry of the hydration process under hydrothermal conditions. The complexity is such that this a grand challenge problem in industrial materials chemistry.

NMR logging and surface relaxivity

NMR logging is providing new information on rock permeability and other properties which depend on the restricted diffusion of spins in the pore space. The diffusing spins see the mineral surfaces and are sensitive to paramagnetic impurities which provide a powerful relaxation mechanism.

Stabilisation of shales: intercalation

Wellbore stability problems in shale formations are slowly being brought under control by new stabilising chemistry. Polyols form stable intercalates with smectites; the efficacy depends greatly on the molecular structure and molecular design based on molecular/atomic surface models is now a reality.

Underlying scientific themes

(1) Characterisation of the surface composition of sedimentary (especially reservoir) rocks; (2) predictive models and associated data on reaction rates (including adsorption, desorption, dissolution and crystal growth; (3) construction of coupled chemical-convective models of porous media flow.