The Heron Clusterfieldsform part ofthe Eastern Trough Area Project,anintegrated development ofa totalofsevenfields. The mainreservoirwithinthe clusteristhe Triassic Skagerrak Formation (withundeveloped Jurassic PentlandF ormation inHeron andE gret). The fieldsarec lassified asHPHT reservoirs,withi nitial pressuresandtemperatureso f9300-12 900 psia nd300-350 8 Frespectively. Development ofthesefi elds initially assumed thatt he Skagerrak wouldb ewell connected andlikely to havea nactivea quifer. However, initialproduction from Heron in1998revealed adramatic pressuredecline, indicatingthatthe reservoirwasmore compartmentalized thananticipated, withlittleor no aquifer,necessitatingarevision to the reservoirmodel. The Skagerrak canbe subdivided into anupper,morechannel-dominated intervalandalower,poorerquality,more unconfined fluvialsection,bounded below bythe largely playaMarnock Shaleandabovebythe lacustrineHeron Shale.Re-description ofthe reservoirs uggested asettingd ominated byt erminals playdeposits,a rranged into cyclesbounded byah ierarchyo fshales,which formed laterally persistent,e ffectiveb arriers to verticalflow. Additionalperforations through the Skagerrak section encountered nearvirginpressuresandrestored production profilestoprognosis. Egretcameon-streamin1999 withasingleverticalwell andagainshowed arapid pressure decline, inthiscaseadditionallydueto fault compartmentalization. However,itwasobserved thatthe reservoir wasr e-chargingd uringshut-inp eriods,suggestingthatt he faults weretransmissiblewithsufficient pressure drawdown. Withe xperience from Heron andEgreto nv erticalcompartmentalization andfault transmissibility, Skuawasbroughton-streamin2001 withasinglehorizontalwell designed to intersectasmuch stratigraphyas possible.The Skagerrak reservoirinSkuaalso exhibits Egret-like rechargingacross faults. Overall the Skagerrak reservoirs inthe Heron Clusterappeartohavethe followingcommon characteristics:goodlateralconnectivity, but poor to zero verticalconnectivity; large faults become'leaky' withsufficient pressuredrawdown,andthere appears to be no aquifersupport. The short term production behaviour ofthesereservoirs isnot representativeof theirlonger-term behaviour,andinparticular,short-term well tests indicatealevelofcompartmentalization that doesnot materializeduringproduction.
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