Tamboesai, Emrizal Mahidin2014-01-232014-01-232014-01-23978-6-0298-9161-4wahyu sari yenihttp://hdl.handle.net/123456789/5308A Production well (X well) in the Thal Area Riau, produce two types of crude oil; light oil and waxy oil. These type oil is obtained from two different strata reservoir that is, A reserroar (1762, 6 m) and B reservoir (1900,5 m). The double string production pipes distribute the crude oil from A reservoar (shortstring) and B reservoar (long string). Two types of methods, ROF GC and biomarker have been used to study reservoar geochemisry of X well. The study showed that there are mix between oil from reservoar A and B. The mix is coused by corrotion in the pipe line. The mix increased from 4 % in 1979 to 95 % in 2001. The reservoar show that Goechemistry rservoar can be applied to prevent even to improve the efficiency of production of X-Well in the futureenGeochemistry reservoarproduction pipesfinger printUR-Scientific Work Lecturer