A correction method for the gamma ray curve of South Pars Block in Iran

Gamma ray logging while drilling is currently one important geo-steering logging technology. Due to the in fluence of many formation or non-formation factors, the gamma ray pipe detection is interfered more by K⁴⁰, so the environmental coefficient shall be corrected. In newly developed blocks (e.g. South Pars Block in Iran), however, on-site operators cannot correct the gamma value accurately for LWD manufacturer cannot offer accurate field correction data and charts. In this paper, optimization fitting analysis and matlab data statistics were carried out on abundant practical data obtained during the directional drilling of Ø311 mm hole in four blocks of South Pars, Iran, including SPDC19-x, SPDC15-x, SPDC4-x and SPDC6-x. And a new correction method was developed and a new gamma calculation formula was established. When KCl drilling fluid system is used, the gamma ray curve plotted on the basis of the new correction method is highly accordant with the gamma value of reference exploration formation, with accordance rate of 95% and error ratio lower than 1%. Obviously, it is much superior to the traditional correction technologies. It has been widely applied to the field correction of over 20 wells in other blocks of South Pars in Iran.