Description[edit]The field is being developed byBP plcand 25% partnerExxonMobil[1]It is the largest offshore production platform in the Gulf, with a processing capacity of 250 thousand barrels per day (40103m3/d) ofoiland 200 million cubic feet per day (5,700,000m3/d) ofnatural gas, and the field is believed to hold in excess of 1 billion barrels (160106m3) of oil.[2]Actual production approached capacity in March 2009, but started to decline soon after that.[3]Discovery and development[edit]The Thunder Horse discoverywellwas drilled in 1999 onMississippi Canyonblock778. It was drilled to a depth of 25,770 feet (7,850m) from thedrillshipDiscoverer Enterprise, hitting three intervals of oil.A second well was drilled in block 822, 1.5 miles (2.4km) southeast of the initial discovery, reaching a depth of 29,000 feet (8,800m) in November 2000 and also encountered three primary intervals of oil.In February 2001 a new field known as Thunder Horse North was drilled in block 776, approximately 5 miles northwest of the original field. This well reached 26,000 feet (7,900m) and again met three intervals of oil.[4]Actually developing the field was a major technological challenge due to the depth of the find. Not only are the distances large, but at such depths the formations holding thehydrocarbonscreate pressures over 1,200bars(120MPa) and temperatures of135 C(275F). Prior to Thunder Horse, no field had ever been developed at such a depth.Following lengthy delays caused by the need to repair and replace components in the subsea system (following a failure during pre-commissioning checks), "First oil" came on June 14, 2008. Since then, Thunder Horse has steadily ramped up its production by bringing on new wells. In March 2009, Thunder Horse produced close to 250,000 barrels per day (40,000m3/d)oil equivalentin oil and natural gas from seven wells. Plans were in place to add two additional wells in 2009 to further develop the north end of the field. By January 2010 the MMS data indicated that total daily production during 2009 had declined from near 250,000 to 175,000 barrels per day (40,000 to 27,800 m3/d).[5][6]The Washington Post noted in May 2010 that "There could be less off-shore oil than the [Obama] administration assumes" quoting an analysis in TheOilDrum.com by Glenn Morton, a consultant for oil exploration projects who stated that "Thunder Horse hasn't reached anywhere near its expected potential," in oil or natural gas a fact which "underscore[s] the point that deepwater oil drilling is a tricky process, and not always as easy or predictable as thought"[7]Thunder Horse platform[edit]Main article:Thunder Horse PDQThunder Horse PDQis the largest mooredsemi-submersibleproductionoil platformin the world, located in 1,920 metres (6,300ft) of water in theMississippi CanyonBlock 778/822, about 150 miles (240km) southeast of New Orleans.Construction costs were around five billionUSD, and the platform is expected to operate for 25 years.[8]Thehullsection was constructed byDSMEinSouth Koreaand delivered in toKiewit Offshore ServicesinIngleside, Texason 23 September 2004 aboardMVBlue Marlinfor completion.[9]Thunder Horse was completed atKiewitOffshore Services in nearbyIngleside, Texas.Thunder Horse PDQwas evacuated with the approach ofHurricane Dennisin July 2005. after the hurricane passed, the platform waslistingbadly. The platform was designed for a 100 year event, and inspection teams found no hull damage, and no water was taken on from a leak through its hull. Rather, an incorrectly plumbed, 6-inch length of pipe allowed water to flow freely among severalballast tanksthat set forth a chain of events causing the platform to tip into the water.[10][11]The platform was fully righted about a week afterDennis, delaying commercial production initially scheduled for late 2005.[12]During repairs, it was discovered that the underwater manifold was severely cracked due to poorly welded pipes. The rig's design engineer, Gordon Aaker, said that the cracked manifold could have caused a catastrophic oil spill.[13]The platform took a near-direct hit six weeks later byHurricane Katrina, but was undamaged.Naming dispute[edit]Originally calledCrazy Horse, BP changed the name out of respect to descendants of theNative Americanwarrior of thesame name. The company said that it acted after the family of theLakotawarrior and spiritual leader told them that use of his name outside of a spiritual context is sacrilegious.[14]

Cross Bedding dan Cross Lamination

Cross-Beddingadalah fitur yangterjadi padaberbagai skala, danteramati padakonglomerat dan batupasir.Hal ini mencerminkanpengangkutankerikildan pasiroleh arusyang mengalirdi atas permukaansedimen(misalnya disaluran sungai).Pasirdi saluransungai ataulingkungan pesisirketikacross-bedding terbentuk, pasirdiangkutseperti pasir-gundukanseperti gelombang pasir, di mana sedimenbergerak naikterkikissepanjanglerengupcurrent, dan terendapkan kembali di lerengdowncurrent.Setelah beberapabedformsbermigrasimelewati area,dan jika ada sedimen diendapkandaripada tererosi,akan adapenumpukancross-bedding lapisanbatu pasir. Kecenderungandaricross-beddingmenunjukkan arah transportasi danaliran arus.Gayadan ukurancross-beddingdapat digunakanuntuk memperkirakankecepatan arus,dan orientasicross-beddingmemungkinkanpenentuanarahpaleoflow.Cross-beddingjuga dapat diproduksiketikaangin bertiupdi atas permukaanpasirdan menciptakanbukit pasir. Laminasi adalah urutan skala kecil lapisan halus (lamina) yang terjadi pada batuan sedimen.Laminasi biasanya lebih kecil dari bedding.Laminasi sering dianggap sebagai setiap struktur planar yang berukuran lebih kecil dari 1 cm, dan bedding sebagai setiap struktur planar lebih besar dari itu. Sebuah batuan sedimen tunggal dapat memiliki baik lamina maupun bedding. Laminasi terdiri dari perbedaan-perbedaan kecil dalam jenis sedimen yang terjadi sepanjang batuan.Laminasi disebabkan oleh perubahan siklik dalam penyediaan sedimen. Perubahan ini dapat terjadi pada ukuran butir, persentase tanah liat, kandungan mikrofosil, kandungan bahan organik atau kandungan mineral dan sering mengakibatkan perbedaan yang menonjol dalam warna antara lamina. Laminasi dapat terjadi sebagai struktur paralel (paralel laminasi) atau di set berbeda yang membuat sudut satu sama lain (cross-laminasi).Hal ini dapat terjadi pada berbagai jenis batuan sedimen, dari batu pasir kasar untuk serpih halus, batulempung atau bahkan di evaporites. Karena laminasi adalah struktur halus, laminasi mudah rusak karena bioturbation (aktivitas menggali organisme) segera setelah pengendapan. Laminasi berkembang pada sedimen berbutir halus ketika partikel berbutir halus menetap, yang hanya bisa terjadi dalam air yang tenang. Laminasi dalam batu pasir sering terbentuk dalam lingkungan pesisir, di mana energi gelombang menyebabkan pemisahan antara butir ukuran yang berbeda. Perbedaan antara high angle cross-bedding dan low angle cross-bedding terletak pada proses pembentukan cross-bedding itu tersendiri. Pada high angle, arus yang mempengaruhi pembentukannya lebih kuat dibandingkan dengan arus lemah yang membentuk low angle cross-bedding. Antidunes yang bermigrasi kea rah hulu juga mengakibatkan low angle cross-bedding.

BATUAN SEDIMEN

BATUAN SEDIMEN

2.1. Struktur SedimenStruktur sedimen termasuk ke dalam struktur primer yaitu struktur yang terbentuk pada saat pembentukan batuan (pada saat sedimentasi). Struktur sedimen dapat dibagi menjadi 4 yaitu : Struktur Sedimen Pengendapan, Struktur Sedimen Erosional, Struktur Sedimen Pasca Pengendapan dan Struktur Sedimen Biogenik.2.1.2. Struktur Sedimen Pengendapan (Depositional Sedimentary Strucures)Adalah struktur sedimen yang terjadi pada saat pengendapan batuan sedimen.Perlapisan/LaminasiPerlapisan adalah bidang kesamaan waktu yang dapat ditunjukan oleh perbedaan besar butir atau warna dari bahan penyusunnya. Disebut perlapisan bila tebalnya >1 cm dan laminasi bila tebalnya