Magnesia cement slurry for water plugging, leak plugging, and temporary plugging of oil and gas well reservoirs and its preparation method

The invention relates to magnesium-oxygen cement slurry used for reservoir water plugging, leak plugging and temporary-closure plugging in an oil and gas well and a preparation method thereof. The cement slurry contains the following components in parts by weight: 100 parts of active magnesium oxide, 50-105 parts of water, 30-100 parts of water-soluble blending agent, 0.5-10 parts of water-soluble borate, 1-8 parts of carbohydrate retarding agent, 0-400 parts of acid-soluble hard filling material, 1-5 parts of fluid loss agent, 0-5 parts of foaming agent and 0-2.5 parts of foam stabilizing agent, wherein the active magnesium oxide is obtained through roasting magnesium carbonate or magnesium oxide at high temperature; the water-soluble blending agent is a mixture which is one or over two of sodium pentaborate, sodium tetraborate and disodium octaborate tetrahydrate; the carbohydrate retarding agent is a mixture which is one or over two of sucrose, lactose and glucose; and the acid-soluble hard filling material is calcium carbonate or magnesium carbonate. According to the invention, a magnesium-oxide cement stone is removed from a stratum layer by using an acidizing way; the damageto the stratum layer is low; and the wide practical value is achieved.