The Diagenesis Of The Sandstone In Chang8-10Layer,Yanchang Formation, Longdong Region,Late Triassic Of Ordos Basin And The Thermodynamics Behavior Of Laumontite

Chang8-10reservoir group, Yangchang Formation, Longdong Region, Late Triassic of Ordos Basin is focused on development of new series of strata in recent years, and its research degree than other oil layer group is not very high. So further study of the formation of petrologic characteristics and diagenesis is necessary.Widely development show even crystal or pore of cementation of laumontite blocked most of the primary pore, but later in the acidic fluid intervention and can cause laumonite dissolution, the secondary porosity laumonite dissolution formed once become a reservoir of oil and gas reservoirs, so the long8-10reservoir group of laumontite cause, forming environment and its relationship with other minerals has important value.Chemical thermodynamics can be made without complex pHysical chemistry experiment simulation, through the mature of the direction of the thermodynamic calculation model of chemical reaction happened, difficulty in chengdu and relationship of pHysical and chemical parameters to make the right judgment. Between this, through chemical reaction of laumontite related reasons, can be further formation of laumonite dissolution mechanism to do some beneficial discussion.Through the discussion, the main knowledge we get is:1. The extended set of combination of sandstone under the main rock types of the lithic arkose, feldspathic sandstone and feldspathic lithic sandstone, particle size is given priority to with fine grained, rounded edges as a condition is given priority to, grain contact relationship is line contact or concave and convex contact more, most of the particles in support, main cement is calcite, chlorite, laumontite, secondary and feldspathic quartz. Calcite formed a pore cementation, laumontite for silicon cementation, quartz and feldspar to increase edge bonding, some inlaid cementation. Porosity and permeability is poor, the main pore types of primary intergranular pore, secondary dissolution pore, microfracture development again, in which solution pores in multiple for feldspar and laumonite dissolution pore.2. The combination of experiences of sandstone diagenesis mainly compaction, pressolution, cementation and dissolution, metasomatism. The early formation of chlorite coated effectively protects the original intergranular pore. A wide range of chlorite and laumonite cementation, fewer kaolinite and quartz increase reflects the weakly alkaline diagenetic fluid environment. Generally sandstone in the study area has reached A-B in the diagenetic stage.3. By means of chemical thermodynamics calculation verification laumontite form need higher pH value, high sodium and calcium ion concentration low potassium ion concentration.4. The reasons for the formation of laumontite mainly volcanic glass hydration, plagioclase albitization next and heulandite dehydration reactions found in sedimentary rock formation environment survive is debatable, but kaolinite with calcium carbonate on generating laumontite reaction thermodynamics is not established.5. Under the same [H+], calcium feldspar, sodium feldspar dissolved laumontite priority, laumontite than potassium feldspar dissolved priority, it saw the next combination of sandstone in the secondary solution pores of feldspar dissolution pore. Calcite and laumontite often showed a negative correlation relationship, may be because the formed, due to turbidity zeolite lower free energy than calcite, more stable, has too much calcium, so the calcite content is low, but when increased co2partial pressure of pore water, laumontite in easier than calcite dissolution and generating calcite, and within a certain range, will calcite precipitation increased as the carbon dioxide increases, so that the content of calcite is higher than laumontite.