GEOCHEMICAL RESPONSES OF CARBONATE RESERVOIR TO UNTREATED LAKE WATER REINJECTION

Exploitation with reinjection is thought to be one of the most effective ways to keep reservoir pressure and mitigate water table decrease, which it's widely encouraged. Reinjection with water from other sources is proposed for carbonate reservoir that is easily to inject. This paper discusses the possibility of reinjection with untreated lake water and geochemical responses of carbonate reservoir based on water-rock interactions experiments for dolomite reservoir of Wumishan Group in Donglihu Area, Tianjin. Results show that after reactions with dolomite, TDS of reacted water decreases indicating that precipitation occurs and the precipitates amounts to 142.6 mg·L^-1, which is equal to 0.09%increase in mineral quality. At the initial stage, plagioclase dissolves and alkaline metals like K、Ca、Na, SiO₂ and Al-bearing compositions were released, leading to oversaturation and precipitations of dolomite, calcite and K-feldspar. With the progresses of reactions, incongruent dissolution causes part of the dolomite dissolves while calcite keeps precipitating. Illite precipitates and its effects on reservoir structure depend on its shape. Based on the experimental data, it's concluded that the dolomite reservoir will slightly be affected by reinjection of lake water and it's still a good way to explore sustainable developments for geothermal exploitation.