Since fossil fuels are still dominant sources of energy supply, in order to meet rising energy demand, petroleum industry is called upon not just to provide an effective management of oil and gas reserves, but also to manage to do that in safe and efficient manner with as low as practically possible ecological footprint. Consequently, also taking into account the fact that conventional oil and gas reserves are declining, petroleum companies are forced to develop and adopt new technologies to increase oil and gas recovery and to expand their upstream activities to still unexploited areas which often implies development of deep- buried oil and natural gas reservoirs characterized with unfavourable reservoir conditions such as high temperature and pressure and even certain amount of impurities.

Croatian experience with the natural gas production from deep- buried reservoirs is based on the development of several gas fields in the north- western part of Croatia. The development of the largest natural gas fields in Croatia, Molve, Stari Gradac and Kalinovac gas fields has begun at the beginning of the 1980's. The main characteristic of all the mentioned fields are extremely unfavourable reservoir conditions with reservoir depth over 3000 m, high initial reservoir pressures (over 450 bar), high temperature (180°C) and significant share of CO2, (10 - 54%) H2S (800 ppm) as well as some other non- hydrocarbon compounds like mercaptans (30 mg/m3) and mercury (1000 - 1500 µg/m3). In the last 25 years in the same region several other gas fields with the similar reservoir conditions were discovered and developed. Today, petroleum industry in Croatia has almost 30 years of experience in processing sour natural gas with well established methodology of auditing processing plant outlet gas influences on the environment. These experiences and future plans regarding this subject will be presented in this paper.

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