Treatment agent for oilfield produced liquid and application of treatment agent in oilfield development

The invention provides a treatment agent for oilfield produced liquid and application of the treatment agent in oilfield development. The treatment agent for the oilfield produced liquid comprises a decalcifying agent, and the decalcifying agent comprises the following components in parts by weight: 5-10 parts of soluble magnesium salt, 10-20 parts of soluble meta-aluminate, 5-10 parts of soluble carbonate and 10-15 parts of a chelating agent. The soluble meta-aluminate can inhibit the hydrolysis of bicarbonate ions and promote the ionization of the bicarbonate ions at the same time. Soluble carbonate can be combined with calcium ions in produced liquid to generate calcium carbonate precipitates so as to be adsorbed and removed by aluminum hydroxide colloid generated by hydrolysis of meta-aluminate, the chelating agent can capture the calcium ions, and the water quality stability is improved through the synergistic effect of the soluble carbonate and the calcium carbonate precipitates. The soluble magnesium s