Exploration drilling of gas wells: techniques and data analysis

Abstract

This thesis presents a comprehensive study of exploratory drilling operations for gas wells, covering the fundamental principles, equipment, procedures, and practical field applications. The work introduces the origin, composition, and classification of natural gas, followed by the exploration process including geological and geophysical methods, with emphasis on seismic techniques and exploratory drilling. A detailed description of drilling rig systems is provided— hoisting, rotary, circulation, power, and safety equipment—along with drill stem testing procedures and well completion techniques. This study compares two exploration wells in Algeria’s Illizi Basin: Well-1 targeting the deep Cambro-Ordovician formation, and Well-2 targeting the shallower Devonian F2. Based on Drill Stem Test (DST) results, Well-1 shows excellent pressure maintenance, rich wet gas, and ultra-light, high-value condensate at high flow rates. Well-2, although a successful discovery, exhibits greater pressure loss, leaner gas, lower liquid yields, and continuous wellhead decline, indicating limited reservoir support. The study concludes that Well-1 is superior and should be prioritized for development, while Well-2 remains viable but requires careful production management. Both wells confirm the basin’s gas potential, and the complete absence of H₂S is a major economic and safety advantage.