Acid fluids reconstruction clastic reservoir experiment in Qaidam saline lacustrine Basin, China

Abstract

The Qaidam Basin is a large salt lake basin on the Tibetan Plateau where oil and gas flow has recently been discovered in lacustrine clastic reservoir; the organic acids released during the evolution of organic matter in saline lacustrine basins could improve reservoirs in certain cases. The alteration of clastic rock reservoirs by the acid fluids is a complicated physical and chemical process. This experiment simulated interactions between the organic acids and the minerals in reservoir rocks in underground temperature and pressure conditions, and analyzed the influences of interactions on pore properties and pore structures and their formation mechanisms. These influences and alterations are divided into dissolution and precipitation interactions. Feldspar, gypsum, ankerite are likely to be dissolved, and calcite can be precipitated by weakly acidic solutions, which occupies some reservoir space. For the gypsum-containing clastic reservoirs, gypsum is more likely to be dissolved and the supersaturated Ca²⁺ generated with gypsum dissolution leads to the precipitation of calcite. The chemical process of ankerite dissolution provides iron ions and magnesium ions to the chlorite forming reaction and the chlorite can easily block the pore throats, leading to decline of permeability.