--> Abstract: Intergranular Pressure Solution During the Diagenesis of Sandstone: Conditions and Controlling Factors, by Wenwu He, David Sparks, and Andrew Hajash; #90124 (2011)
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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Intergranular Pressure Solution During the Diagenesis of Sandstone: Conditions and Controlling Factors

Wenwu He1; David Sparks2; Andrew Hajash2

(1) Research and Engineering, M-I SWACO, Houston, TX.

(2) Department of Geology and Geophysics, Texas A&M University, College Station, TX.

Intergranular pressure solution (IPS) is regarded as an important mechanism of diagenesis for quartz sandstone. It is caused by stress-induced dissolution at grain Previous HitcontactsNext Hit and diffusion down concentration gradient between grain Previous HitcontactsNext Hit and pore Previous HitfluidNext Hit. But observations of natural sandstone indicate that the diagenetic role of IPS varies widely. Some sandstone shows well-developed pressure-solution structure while others have no visual evidence for IPS. To understand the conditions and controlling factors of IPS in diagenesis of sandstone, we study the dynamic processes at grain Previous HitcontactsNext Hit and in pore Previous HitfluidNext Hit in compacting sandstone. The equilibrium concentration at grain Previous HitcontactsNext Hit (ceqb) increases with stress, which depends on contact area. Therefore ceqb is independent of grain size, but is a strong function of strain. Calculations using experimental creep compaction rate and pore-Previous HitfluidNext Hit chemistry at 150°C and 34.5 MPa of effective pressure as input indicate that ceqb is within one order of magnitude higher than the hydrostatic equilibrium concentration (ceq) at the initial stages of creep compaction. ceqb decays rapidly with increasing compaction and becomes close to ceq after several percent strain. The evolution of ceqb is consistent to that of creep-compaction rate, both of which suggest a fast-decaying creep. The Previous HitfluidNext Hit-chemistry features at stressed grain Previous HitcontactsNext Hit suggest that IPS is very sensitive to pore-Previous HitfluidNext Hit chemistry. To have a well-developed IPS, pore-Previous HitfluidNext Hit concentration is required to be close to saturated or undersaturated. Even a slight supersaturation in pore Previous HitfluidNext Hit could prevent the diffusion along grain Previous HitcontactsNext Hit. Therefore, Previous HitfluidNext Hit flow in sedimentary basins might be an important controlling factor for IPS. Long-term descending Previous HitfluidNext Hit flow (undersaturated due to heating up) could result in well-developed IPS while ascending fluids (supersaturated due to cooling) would inhibit IPS. Mineral reactions in natural sandstone, such as feldspar alteration, could create a pore Previous HitfluidTop supersaturated in silica, which would favor quartz cementation or overgrowth. Therefore, strong mineral alteration and the corresponding quartz cementation or overgrowth may suggest a poorly-developed IPS.