Zdenko Krištafor

Long-lasting Experience In Environmental Protection During Sour Gas Reservoir Exploitation

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 1980s. 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.

DOPRINOS METODOLOGIJI ODREĐIVANJA OPTIMALNE GUSTOĆE ISPLAKE – PRIMJER IZ PRAKSE IZRADE BUŠOTINA S ODOBALNOGA PLINSKO-KONDENZATNOG POLJA D U PERZIJSKOME ZALJEVU

Drilling the wells using water based mud through shale formations, causes their exposure to serious time-dependent wellbore instability due to shale swelling. Operating companies, before drilling operations through demanding shale formations, usually conduct drilling uid optimization studies in order to de ne the proper mud type, mud density, salt type and concentration for inhibition. Through the analysis of o set wells, they are interpreting data about mud ltrate breakouts into the rock formations and chemical potential mechanisms to understand their in uence on the time-dependent wellbore instability. The main objective of this paper is to give an insight in time-dependent and mechanical wellbore instability problems faced while drilling the wells through di erent shale formations in the gas condensate eld D in the Persian Gulf. The importance of drilling uid design optimization and solutions applied to overcome hole instability problems were analysed and highlighted. Besides the development of a model for mud density calculations, a concept of e ective hoop stress and its in uence on time dependent failure mechanisms is discussed. As a contribution to the method improvement, mud density calculation is veri ed by taking into the consideration the relationship between pore pressure and e ective hoop stress and it is based on measured data from Well A in gas condensate eld D from the Persian Gulf.

Sour-Gas-Reservoir Exploitation in Croatia

Because fossil fuels are still dominant sources of energy supply, the petroleum industry is called upon not only to provide an effective management of oil and gas reserves in order to meet rising energy demand, but also to do that in a safe and efficient manner, with as small an ecological footprint as practically possible. 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 by unfavorable reservoir conditions such as high temperature and pressure and even a certain amount of impurities. Croatian experience with natural-gas production from deep-buried reservoirs is based on the development of several gas fields in the northwestern part of Croatia. The development of the largest natural-gas fields in Croatia--Molve, Stari Gradac, and Kalinovac gas fields--began at the beginning of the 1980s. The main characteristic of all the mentioned fields are extremely unfavorable reservoir conditions, with reservoir depth of more than 3000 m, high initial reservoir pressures (more than 450 bar), high temperature (180°C), and a significant share of CO2 (10 to 54%), H2S (800 ppm), and some other nonhydrocarbon compounds such as mercaptans (30 mg/m3) and mercury (1000 to 1500 μg/m3). Several other gas fields with similar reservoir conditions were discovered and developed in the last 25 years in the same region. Today, the petroleum industry in Croatia has almost 30 years of experience in processing sour natural gas with a 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.

Injection Technology For SustainableEnvironmental Protection In ThePetroleum Industry

Since, petroleum industry is considered to be one of the main environmental polluters, increased attention is put on environmental protection during petroleum activities for minimising their negative environmental impact. During exploration, well stimulation and oil and gas production a certain amount of reservoir brine, solids and other wastes are produced. By using injection technology petroleum industry waste is injected into suitable underground geological formations, from where it originated and it is safely removed from the human biosphere. With this injection technology, both the liquid and solid phases are deposited simultaneously and safely into the selected formation. Compared to the injection technology, surface disposal of petroleum industry waste, along with its technological imperfections, is much more expensive and more environmentally intensive. This kind of waste disposal technology has been known and implemented for more than half a century in developed countries. For the last two the same technology has also been used in Croatia. At this moment, petroleum industry waste is in Croatia injected just at one oil field, but there are several projects that consider wells and geological structures suitable for disposal of this kind of waste. With the negative publicity regarding environmental impact in the past, and considering the new set of environmental laws and standards, the waste injection technology could be the solution for the petroleum industry on how to achieve sustainable waste management and diminish its impact on environmental balance that is predicted to be even greater. Furthermore, implementation of injection technology could also be the solution for greenhouse gas problem.