شناسایی هیدروکربن نفتی با استفاده از ارزیابی ژئوشیمیایی گل حفاری و نگارهای پتروفیزیکی در سازندهای کنگان و دالان

سازندهای کنگان و دالان به‌دلیل عمق تدفین زیاد همیشه به‌عنوان مخازن گازی در نظر گرفته شده‌اند. این مطالعه به‌بررسی نوع سیال هیدروکربنی موجود در مخازن کنگان و دالان براساس تفسیر ژئوشیمیایی گاز محلول در گل حفاری همراه با ارزیابی پتروفیزیکی در یکی از چاه‌های حفاری شده دور از ساحل خلیج‌فارس پرداخته است. برای رسیدن به این هدف، مطالعه در سه مرحله صورت پذیرفته است. در مرحله اول ارزیابی پتروفیزیکی با فرض کل مخزن به‌عنوان مخزن نفتی انجام گرفت. در مرحله بعدی نوع سیال براساس تفسیر ژئوشیمیایی گاز محلول در گل حفاری با استفاده از روش‌های هاورث و پیکسلر شناسایی شد. نوع سیال نهایی براساس انطباق هر دو روش تعیین گردید. در مرحله آخر نیز ارزیابی مجدد پتروفیزیکی در بخش نفتی مستعد انجام گرفت. براساس تفسیر اولیه پتروفیزیکی، سه بخش نفتی شامل k1، k2 و k4 در مخزن وجود دارد. با این حال، براساس تفسیر ژئوشیمیایی گاز محلول در گل، دو بخش k1 و k4 گازی بوده و فقط بخش k2 حاوی هیدروکربن نفتی است. ارزیابی نهایی پتروفیزیکی بخش k2 به‌عنوان بخش نفتی، تخلخل مفید 6% و اشباع شدگی 29% را نشان داد. نتایج حاصل از این مطالعه آشکار ساخت که توجه به تفسیر ژئوشیمیایی گازهای محلول در گل حفاری در تعیین بازه مناسب مشبک‌کاری و همچنین انتخاب بخش‌های مناسب جهت انجام تست‌های مخزنی باعث کاهش هزینه و زمان نهایی حفاری خواهد شد.

identification of oil type hydrocarbon using mud gas logging and petrophysical logs evaluation in the kangan and dalan formations

introduction organic geochemistry, as a branch of multidisciplinary science, has experienced significant advances. part of these advances has been due to technological progress in production of laboratory instruments and the others due to development of applied software in this branch [1]. one of the major progresses of this branch has taken place in hydrocarbon exploration and, more recently, in the optimized management of hydrocarbon reservoirs [2].the present study was carried out in a well in one of offshore fields in the persian gulf. this well was completed in kangan and dalan formations. the kangan formation in this field comprises two third order sequences of the upper kangan (k1) and the lower kangan (k2). the dalan formation is divided by the nar anhydrite member into two parts: the upper dalan (which is itself divided into two third order sequences of k3 and k4) and the lower dalan (sequence k5). in this well, both kangan and dalan formations were completely drilled and complete petrophysical and mud-logging data from them were gathered and available. in this study, production zones and the type of hydrocarbon fluids of the kangan and dalan formations were investigated, and the results of geochemical evaluation of the associated gas with drilling mud and petrophysical logs are considered as well.materials and methodsin this study, mud-logging data and petrophysical logs from a well in the dehram group were studied. initially, the studied interval was petrophysically evaluated. subsequently, the mud-logging data of drilling mud gas were studied. then, the results from both methods were compared, and the type of hydrocarbon in the studied intervals was interpreted. eventually, the interpreted interval was re-evaluated using petrophysical analysis.• pixler method in defining the type of hydrocarbon and production zonein 1969, pixler introduced a method that utilized the ratios of c1/c2، c1/c3، c1/c4, and c1/c5 gainedfrom gas chromatography analysis of the gases present in drilling mud for interpretation of reservoir fluids. the pixler diagram consists of four fields: one field for oil, one field for gas and two fields for non-productive parts. in fact, location of the introduced ratios within each field represents the presence of oil zone, gas zone or an uneconomical reserve.• haworth ratios for defining the productive zone and the type of hydrocarbon in this method, the concentration of c1 to c5 gaseoushydrocarbon is used for calculation of wetness ratio(%wh), balance ratio (bh) and character ratio (ch)factors [3]. the wetness index equals the percentageratio of wet gases (c2 to c5) to total gases (c1 to c5).the balance factor is the ratio of light gases (c1 andc2) to heavy gases (c3 to c5) and the character ratiouses the concentration of c1 to c5 for interpretinghydrocarbon shows regarding gas cap, o/g contactand water saturated zone [4].results and discussionthe kangan and dalan formations have been alwaysconsidered as gas reservoirs due to their high burial