Bu Parvita, Koreksi overburden seharusnya dilakukan. Kalau kata sumber yg bisa dipercaya sih "Overburden correction can reduce the porosity from 0.5-1.0 p.u. (ratio: 0.90-0.97):.jadi setelah koreksi, porositas-nya bisa 0.9-0.97 kali dari awalnya. Archie Formula:(Sw^n)= FF(Rw/Rt)Jika Sw= 100% maka Ro=RtFormation Factor=a/(porositas^m)=Ro/RwResistivity Index=RI=1/(Sw^n)=Rt/R0 Dari rumus di-atas sudah jelas bahwa porositas cukup menentukan dalam Electrical Measurement CCAL. Dari sumber yang bisa dipercaya: nilai m setelah koreksi overburden= nilai m ambient+0.05 sampai nilai m ambient+0.1 (ratio 1.05-1.1). jadi setelah dikoreksi akan didapatkan nilai m yang lebih besar. Sumber kesalahan dari kalkulasi porositas CCAL: pencucian, pengeringan,pengukuran reservoir stress, jenis texture, Representavity/homogeneity. Pengeringan pada suju 80 degC seringkali menyebabkan mineral lempung rusak (shale collapse) sehingga menambah nilai porositas. Disarankan di suhu 60 degC saja, nggak usah panas2.
Ketidakpastian nilai m:- Error porositas versus error m- m overburden versus m ambient (nilai m meningkat sebanding dengan porositas)- Plugs anisotropy (bedding, fissures, conductive minerals, dll) Ketidakpastian nilai m:-Plugs harus di_de-saturated- Jangan pakai plugs apabila Sw mini > 40-50%.- Error pada porositas --> error pada Sw --> eror pada nilai n- Hysteresis on RI ; Sheath effect on Pc and RI yang akan menghasilkan artificial porositas hingga 2 kali lipat (Swanson, 1985) Berikut ada rujukan tambahan:----FORMATION RESISTIVITY MEASUREMENTS(Core Lab, 2007, Application of Core Analysis In Reservoir Description & Characterisation) MethodsResistance is measured and converted to resistivity of the 100% or partially brine-saturated sample. Tests normally made at ambient temperature and net overburden pressure can be simulated.---Effect of Overburden Pressure on Resistivity(Buku: Torsæter & Abtahi, 2003, RESERVOIR ENGINEERING LABORATORY WORK BOOK, Norwegian University of Science and Technology)Confinement or overburden pressure may cause a significant increase in resistivity. Thisusually occurs in rocks that are not well cemented and in lower porosity rocks. Archie, asmentioned before, reported results of correlating laboratory measurements of formationfactor with porosity in the formF m _6.11_ __ _Wyllie investigated the influence of particle size and cementation factor on the formationfactor of a variety of materials. He concluded that the cemented aggregates exhibit agreater change in formation factor with a change in porosity than the unconsolidatedaggregates. Then, the general form of the relation between formation factor and porosityshould beF a m _6.12_ __ _where m is a constant depending on cementation and a a constant controlled by theporosity of the unconsolidated matrix prior to cementation. Salam,YES Sent from my BlackBery® wireline handheldSinyal Bagus Indonesia, Nyambung Teruuusss...! --- On Wed, 6/15/11, Parvita Siregar <[email protected]> wrote: From: Parvita Siregar <[email protected]> Subject: [iagi-net-l] Formation resistivity factor (a, m, n) To: "[email protected]" <[email protected]> Date: Wednesday, June 15, 2011, 1:40 AM Teman2, Di dalam SCAL, ada perhitungan formation resistivity factor a, m dan n yang digunakan dalam petrophysics nantinya. Di dalam pengukurannya, ada yang diukur dalam lingkungan ambient, ada yang di lingkungan overburden (formation pressure). Apakah biasanya teman2 melakukan kedua-duanya dalam analisa atau hanya melakukan yang overburden? Biasanya berapa banyak selisihnya, apakah sensitif? Terimakasih banyak, Parvita H. Siregar Chief Geologist Salamander Energy Indonesia Suite 1502, Indonesia Stock Exchange Bld. 15th Fl, Tower 2 Jln. Jend. Sudirman Kav. 52-53 Jakarta 12190, Indonesia Tel: +62 21 5291 2900 fax: +62 21 3000 4020 mailto: [email protected] P Please consider the environment before you print Disclamer: This email (including any attachments to it) is confidential and is sent for the personal attention of the intended recipient only and may contain information that is priviledged, confidential or exempt from disclosure. If you have received this email in error, please advise us immediately and delete it. You are notified that using, disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited.
