Preview only show first 10 pages with watermark. For full document please download

Spg Paper

spg paper

   EMBED


Share

Transcript

  Production management of oil pools of Sobhasan Complex, Mehsana, NorthCambay Basin C. P. S. Rawat*, Saurabh Pandey** and Jainath Ram****KDMIPE, ONGC, Dehradun ** Mehsana Asset, ONGC, Mehsana *** IRS, ONGC,AhmedabadCorresponding author email: [email protected] Extended Abstract Cambay Basin situated in the north western margin of the Indian Pre-Cambrian shield is a NNW-SSE trending narrow elongated rift basin. Cambay Basin has been subdivided into fivetectonic blocks viz. Sanchor-Patan, Mehsana-Ahmedabad, Tarapur-Cambay, Jambusar –Broachand Narmada-Tapti blocks. Sobhasan Complex is a part of the Mehsana-Ahmedabad tectonic block and comprises of six fields viz. Sobhasan, West Sobhasan, South Sobhasan, Mewad, SouthMewad and Kherwa. Hydrocarbon accumulation in Sobhasan Complex is established in multiplelayers of Kalol, Sobhasan, BCS (Bottom Coal Sand) and Mandhali sands. Mandhali sands of Kadi Formation have wide extension and these sands/silts are tight in nature. Mandhali sands are producing under depletion drive mechanism. BCS sands having good reservoir characteristics are producing under gas cap, depletion and edge water drive mechanism. Sobhasan sands are quitewide spread and having good reservoir characteristics and are producing under mixed anddepletion drive mechanism. Kalol sands are producing under active water drive mechanism. Introduction Sobhasan complex situated in Mehsana-Ahmedabad tectonic block of Cambay Basin ishaving an aerial extent of ~40 km 2 . It extends from Bhandu village in the north of Mehsana cityto Dholasan village in the south. Sobhasan field (Fig. 1) was discovered in 1968 and commercial production started in 1969. Multiple hydrocarbon bearing layers has been established inSobhasan Complex. Mandhali pays are the lowermost of the hydrocarbon bearing layers andhave been divided into nine major layers which have been further subdivided into twenty twolayers. BCS is producing from two layers. Sobhasan sands are the major producing layers andhydrocarbon is distributed in seven layers. Kalol sands are the youngest producing layers andhydrocarbon is distributed in six layers.    Figure 1: Location map of Sobhasan Complex and adjoining fields of the Cambay BasinGeological set up Sobhasan complex is the northern part of the Mehsana-Ahmedabad tectonic block. NNW-SSE trending Mehsana horst subdivides the Mehsana sub-block into two depressions.Sobhasan complex in the eastern part of Mehsana horst is a NNW-SSE trending prominentanticlinal closure with number of independent culminations. Warosan low considered to be thesource kitchen for hydrocarbon generation for sands of Sobhasan complex separates it from theeastern basin margin faults. To the west of Mehsana horst the basin is shallow. Generalisedgeological set up is tabulated below.  AgeFormation/MemberThickness(m)Generalized LithologyDepositionalEnvironment Recentto Sub-RecentGujaratAlluvium (100-400)Sand, Clay and loose gravelFluvialMiocene Jhagadia (100-300)Dominantly sand withclay/claystone intercalationsFluvialKand (100-300)Mainly claystone with minorsandFluvialBabaguru(100-300)Mainly sand with minor clayFluvialOligocene toUpperEocene Tarapur (100-150)Shale with minor sandMarineMiddleEoceneKalol (150-200)Sandstone ,coal and shaleDeltaicEarlyEoceneUpper Tongue(50-100 )ShaleMarineMehsana/Sobhasan (100-250)Sand, Shale and Coal Fluvial toDeltaicLower Tongue(10-40)ShaleMarineMandhali (150-400Sand,Siltstone,Shale andminor coalPro-deltaOCS (OlderCambay Shale)(150-250)Mainly Shale withSand/Siltstone lenses.MarinePaleoceneOlpad (50-1500) Trapwash,Conglomerate,ClaystoneFluvial/AlluvialLateCretaceousDeccan TrapMainly BasaltVolcanic  Production Management Kalol, Sobhasan, BCS and Mandhali sands are established hydrocarbon pools. Due to diversereservoir characteristics of these producing sands different production management measures areapplied to optimize the production. Production performance of Sobhasan Complex sinceinception is given in figure 2. Fig. 2: Production performance of Sobhasan Complex since 1969Kalol Sands : Kalol sands developed between Tarapur Shale and Upper Tongue is major  producing sands and mainly developed in South Sobhasan, Sobhasan and Mewad fields. Six oil producing sands have been identified (KS-I to KS-VI). Bulk of the production is realized from 02004006008001000120014001600180020001969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 2008 2011  YEAR-----> 0255075100125150175200225250 Qo, tpdWC, %No. Of Wells