Radial Thermal Legacy of Drilling Circulation in Early Drill Stem Testing of High-Temperature Wells

• Wei Zhang

  采矿工程学院, 辽宁工程技术大学, 玉龙路88号, 阜新市, 辽宁省, 中国

  Author

• Jun Li

  资源与环境工程学院, 安徽理工大学, 舜耕中路168号, 淮南市, 安徽省, 中国

  Author

• Hao Chen

  安全工程学院, 黑龙江科技大学, 松北大道2468号, 哈尔滨市, 黑龙江省, 中国

  Author

Drilling circulation can leave a persistent temperature disturbance in the rock surrounding a wellbore, and that disturbance may remain active during the earliest stages of shut-in recovery, perforation, cleanup, and drill stem testing. In high-temperature wells the effect is especially important because the contrast between circulating fluid and undisturbed formation temperature is often large enough to create a substantial cooled near-wellbore region. When flow begins before that region has thermally recovered, the entering fluid does not represent the undisturbed reservoir state. Instead it carries the imprint of a radially distributed thermal disturbance whose magnitude and radial extent both evolve with time. The resulting bottom-hole pressure and temperature response is therefore shaped by hidden thermal recovery as well as by the hydraulic behavior of the test. This paper develops a technical framework for reconstructing that hidden radial thermal legacy and for linking it to early drill stem test interpretation. The formulation combines radial heat diffusion in the formation, transient interval entry conditions, temperature-dependent fluid-property effects, and reduced wellbore thermal transport. A compact state representation is introduced for the disturbed near-wellbore zone, and a pressure-temperature inversion is used to recover the hidden entry condition from observed test data. Particular attention is given to multirate tests, because changes in flow rate alter the radial weighting through which the hidden thermal field is sampled. The analysis derives the forward equations, the reduced inversion architecture, asymptotic observability results, and a field-oriented validation procedure designed to quantify entry-temperature bias, interval ambiguity, and uncertainty during the earliest portion of the test.

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