A Kinetic Model of Pressure Solution/Compaction for Porosity Prediction

LAHANN, RICHARD W., Conoco Exploration Research, Ponca City, OK

A pressure/temperature history model for prediction of porosity of well-sorted, quartzose sandstones was developed and calibrated. The model assumes that porosity loss of quartzose sandstones is by pressure solution, which can be modeled by calculations of pressure solution/compaction of a uniform grain pack. The model assumes that all mass mobilized by the pressure solution is precipitated within the system and no mass is introduced from outside sources. A pressure solution rate law was developed that requires depth, temperature, and pressure information throughout the sandstone burial history. Rate of pressure solution is assumed to be proportional to effective lithostatic pressure, inversely proportional to the contact area between grains, and to have an Arrhenius-type dependence o temperature. The predicted porosities vary as a function of grain size and the pressure/temperature history of the sample. "Unknowns" in the rate law were determined by calibration to a North Sea/Norwegian shelf data base of average porosities for well-sorted sandstones ranging in age from Devonian to Jurassic. Comparison of observed and model-predicted porosities indicates that, for the calibration data base, the model has a standard error of estimate of 3.6 porosity units. Sources of error include erroneous model assumptions, and grain size, sorting, and temperature and pressure history determinations on the calibration set. The model was tested on U.S. Gulf Coast Miocene and Oligocene reservoirs and provided good estimates of observed porosities.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)