Metode perhitungan yg digunakan untuk mengetahui water drive strong atau weak, adalah dengan menggunakan material balance method. Saya ada contoh perhitungannya dalam excel (kalo tertarik bisa contact saya via Japri). Untuk menghitung aquifer size volume, ada beberapa method yg bisa dipakai spt : dengan metode Fetkovich atau Carter Tracy. Observasi yg paling sederhana untuk mengetahui apakah water drive yg ada di reservoir kita strong atau weak adalah dengan melihat reservoir pressure trend dan kandungan water cut setelah reservoir kita produksikan.

Tanya – Ihwan Rosyadi

Salam,

Mohon penjelasannya berkenaan dengan batasan water drive dikatakan weak atau strong, kemudian bagaimana menganalisanya? data apa aja yang sekiranya diperlukan untuk analisa tersebut? Atas tanggapanya saya ucapkan terimakasih.

Tanggapan 1 – Heru Danardatu

Pak Ihwan,

Analisanya bisa dilakukan dengan metode material balance.
Agak panjang lebar untuk dijelaskan di sini. Paper SPE nomer 75354 mungkin bisa membantu, plus aplikasinya.

Singkatnya untuk mengetahui kuat tidaknya water drive, kita bisa plot F/Et vs. F (semua ini terminologi material balance).

Dimana:

F = Np(Bt+Bg(Rp-Rsi))+WpBw

dan

Et = Eo+mEg+Efw

Kalau plotnya garis horizontal, berarti tidak ada aquifer-nya.
Kalau ada trend menaik bersamaan dengan membesarnya F, berarti ada aquifer.
Kuat tidaknya berdasarkan bentuk plotnya – analisa ini lebih ke arah visual, kualitatif.

Terlampir ada plot-nya.
Moderator, minta diijinkan ya.. Semoga membantu, nggak nambah bingung.

Tanggapan 1 – Zein Wijaya

Pak Ihwan,

Metode perhitungan yg digunakan untuk mengetahui water drive strong atau weak, adalah dengan menggunakan material balance method. Saya ada contoh perhitungannya dalam excel (kalo tertarik bisa contact saya via Japri). Untuk menghitung aquifer size volume, ada beberapa method yg bisa dipakai spt : dengan metode Fetkovich atau Carter Tracy.

Observasi yg paling sederhana untuk mengetahui apakah water drive yg ada di reservoir kita strong atau weak adalah dengan melihat reservoir pressure trend dan kandungan water cut setelah reservoir kita produksikan.

– Reservoir Pressure cenderung stabil dan ada kenaikan water cut, kita bisa mengatakan bahwa reservoir kita mempunyai strong water drive

– Reservoir pressure cenderung menurun, kita bisa mengatakan reservoir kira mempunyai weak water drive

Observasi sederhana ini dapat kita lakukan dengan catatan: kalo kita yakin drive mechanism di reservoir kita hanya dari water drive (Tidak ada original gas cap)

Pada umumnya ada beberapa jenis drive mechanism di reservoir :

– Solution-gas drive gas dissolved in oil

– Gas-cap drive free gap cap under pressure

– Water drive hydrostatic/hydrodynamic pressure and compressed water

– Gravity drainage density differences of fluids

Berikut saya forwardkan informasi umum mengenai water drive reservoir.
Detail Data data yg diperlukan untuk menganalisa water drive mechanism, mungkin via japri saja..karena ada beberapa excel attachment yg bisa dijadikan referensi.

Water Drive

Often the hydrocarbon accumulation in a reservoir is in contact with a large volume of water-saturated, permeable reservoir rock. Geologically, the volume of the water reservoir or aquifer may be many times larger than the volume of the hydrocarbon reservoir, and extend over a large area. In some cases, the rock may actually outcrop at a point where constant recharging of the aquifer is possible.
As oil and gas are produced from such a system, the water in the aquifer may expand to replace the volume of oil and gas removed. If oil is produced at a rate that is about equal to the ‘activity,’ or response of the aquifer, the reservoir pressure remains at or near its original value and such a reservoir is said to have an active water drive. This natural water influx provides a very efficient recovery mechanism, particularly if the producing wells can be located to drain the maximum area effectively. Water influx can ‘water out’ wells as the invading water reaches a well and the volume of water produced with the oil increases. Eventually the fraction of oil produced drops below an economic level and the well must be shut in or recompleted at a higher interval. Water, like gas, can be ‘coned’ upward into a well, and so production rates must be monitored to control the amount of coning that takes place. Figure 1 shows a typical production history of a water drive
reservoir. d(‘G1241F01′,’Figure 1’)

Figure 1

As we can see, the decline in reservoir pressure with production is very slight. In fact, for a strong water drive and low production rates, the reservoir pressure may remain essentially unchanged. Because the pressure does not drop, the producing GOR remains at or near the initial solution gas-oil ratio. The oil rate will remain at a relatively stable level until the encroaching water begins to reach the producing wells. As production continues, the overall water cut will increase and eventually all wells may water out.