Sandstone matrix

In some composites, filler and matrix are in direct contact with each other. An example from nature is a sedimentary rock, in which pebbles and small rocks (the filler) are embedded in a sandstone matrix. In many composites, however, there is an intermediary zone—an interphase—between filler and matrix. An example of an interphase is the adhesive that holds filler and matrix together in a laminated (layered) composite. 

Influence of Sandstone Matrix Composition. Some of the sandstones investigated contain a notable quantity of feldspar. It has been confirmed that there is a clear correlation between the composition of the sandstone matrix and pressme solution. The... 

Theoretically, acid flows through the pore system, dissolving solids and flnes entrained in pore throats and pore spaces that impede oil or gas flow. Figure 2-1 depicts acid flow through a sandstone matrix pore system. As acid flows through pore channels, it is presumably able to dissolve small flnes and particles present in pore spaces, pore throats, and along pore walls. 

Fig. 2-1. Acid flowing through a sandstone matrix pore system...

Formation cementation may be carbonate mineral or clay. If a sandstone matrix is held together primarily by carbonate, treatments with acid solutions containing appreciable HCl or organic acids may substantially remove this mineral phase, resulting in sand production and severely impaired productivity. Expensive workover operations will likely be required in such a case. 

This is particularly the case with sandstone matrix formations. In carbonates—and perhaps in naturally fractured reservoirs— there is a greater stimulation potential through an undamaged formation. However, just the same, significant stimulation cannot be expected in any undamaged formation—sandstone or carbonate, matrix or naturally fractured. 

The tables in this appendix present successful, generalized treatment procedures for sandstone matrix acidizing. The examples encompass a variety of applications and conditions. 

Carbonate rocks are more frequently fractured than sandstones. In many cases open fractures in carbonate reservoirs provide high porosity / high permeability path ways for hydrocarbon production. The fractures will be continuously re-charged from the tight (low permeable) rock matrix. During field development, wells need to be planned to intersect as many natural fractures as possible, e.g. by drilling horizontal wells. 

Pulpstones. Improvements have been made in the composition and speed of the grinding wheel, in methods of feeding the wood and pressing it against the stone, in control of power to the stones, and in the size and capacity of the units. The first pulpstones were manufactured from quarried sandstone, but have been replaced by carbide and alumina embedded in a softer ceramic matrix, in which the harder grit particles project from the surface of the wheel (see Abrasives). The abrasive segments ate made up of three basic manufactured abrasive siUcon carbide, aluminum oxide, or a modified aluminum oxide. Synthetic stones have the mechanical strength to operate at peripheral surface speeds of about 1200—1400 m /min (3900 to 4600 ft/min) under conditions that consume 0.37—3.7 MJ/s (500—5000 hp) pet stone. 

A reservoir is not a subterranean lake of pure oil or a cavity filled with gas. It is a porous and possibly fractured rock matrix whose pores contain oil, gas, and some water, or else, more rarely, it is a highly fractured rock, whose fractures contain the fluids. Such a resewoir is usually located in sandstone or carbonate rock. The rock matrix of an exploitable reservoir must be porous or fractured sufficiently to provide room for the hydrocarbons and water, and the pores and fractures must be connected to permit fluids to flow... 

Figure 1. Micrograph of foam in a 1.1 pm, two dimensional etched-glass micromodel of a Kuparuk sandstone. Bright areas reflect the solid matrix while grey areas correspond to wetting aqueous surfactant solution next to the pore walls. Pore throats are about 30 to 70 /xm in size. Gas bubbles separated by lamellae (dark lines) are seen as the nonwetting "foam" phase.

These unconformity-type deposits are located around the unconformity between the Helikian Athabasca Group sandstones and underlying Archean to early Proterozoic metamorphic basement (Hoeve Sibbald 1978 Hoeve Quirt 1984). The present sandstone cover ranges from 0 to 1500 m in thickness and is dominantly composed of mature coarse-grained quartz arenite with a kaolin-illite clay matrix. 

Conglomerate is a mechanical sediment made of rounded clasts of pebble to cobble size in a finer-grained matrix. In a sedimentary breccia the clasts are angular. In both of these types of rocks, the clasts must make up at least 25% of the volume. Rocks with fewer clasts would be classified by the matrix. For instance, a sandstone with a few rounded clasts could be called a pebbly sandstone. 

Figure 7 Replacement driven by force-of-crystal-Uzation is characterized by authigenic phases that develop euhedral faces that are not plausibly constmed as crystal growth within pore spaces (a) sphalerite replaces albitized detrital feldspar and adjacent portions of clay-rich matrix, Frio Formation, Oligocene, South Texas and (b) siderite crystal (s) attacks a detrital K-feldspar (K) in sandstone, Breathitt Formation, Pennsylvanian, eastern Kentucky.

This matrix acidization process consists of injecting hydrochloric acid (for limestones) or a hydrochloric acid-hydrofluoric acid mixture (for sandstones) into the formation pore space. The acid reacts with and dissolves portions of the original rock matrix and thus increases permeability. The depth that the acid penetrates into the formation is one of the factors that determines the effectiveness of the treatment. 

Very simply, a sandstone has a grain composition of stone detritus (quartz, feldspar, detritic mica/clays) and a binder that may be clayey, quartzitic, or carbonatic (or mixtures thereof) [51, 55]. The mineral composition of limestone is mostly calcium carbonate, often derived fi om precipitated calcium carbonate and fossil shell remnants fi-om marine organisms and a calcitic binder matrix [51, 56, 57]. 

Faults in sandstones deformed at depths greater than 1 km tend to deform by cataclasis. Permeability and entry pressure of such faults can be predicted from estimates of matrix properties. Static seal capacities of cataclastic faults depend on the minimum sealing properties, which are related to the fault displacements. 

By examining grain size and mineralogical composition of the fault zones it is clear that the material herein was derived from the channel sandstones (Sverdrup and Prestholm, 1990). Variations in grain size and matrix content define the fault-parallel lamination. The undeformed sandstones and the fault zones both have porosities in the range between 0 and 5%. Additional field observations and textural char-... 

The Yellow Brumunddal Sandstone is a Triassic, predominantly aeolian sandstone, with pronounced anisotropic properties, and with feldspar that has been weathered to clay. The average porosity is 14%, and the matrix permeability varies between 3.8 mD (perpendicular to bedding planes) and 35 mD (parallel to bedding planes). The average uniaxial compressive strength is 19 MPa. 

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