Batuan klastik, terminologi ‘clay’, ‘silt’, ‘sandstone’, ‘conglomerate’, etc., merupakan klasifikasi berdasarkan dominasi UKURAN BUTIR matriks penyusun batuannya, jadi, tidak dipengaruhi oleh komposisi mineraloginya. Ringkasnya, bisa saja reservoir yg didsikripsi sebagai ‘sandstone’ tsb memiliki komponen penyusun matriks detrital carbonate, nah batupasir / sandstone ini yg secara geologi dinamakan sebagai ‘calcarenite’. Batuan jenis ini biasanya terbentuk tidak jauh2 dari host rock carbonate body, ingat, detrital carbonate tidak bisa ditransport jauh, materialnya sangat rapuh, berbeda dengan kuarsa.

Tanya – Filipus Aron

Dear All,

Mohon bantuannya mau bertanya mengenai masalah perpasiran dan reservoir :

Apakah mungkin suatu reservoir sandstone namun memiliki pasir yang ternyata adalah karbonat?

Bila suatu lapangan mengalami masalah perpasiran, bagaimana rumus untuk menghitung rate produksi minyak maksimal tanpa menyebabkan pasir terproduksi?
Terimakasih untuk bantuannya.

Tanggapan 1 – romi faesa

Saya coba sedikit menjawab:

1. afaik, tidak mungkin.

2. Coba lihat persamaan Stoke. saya lupa detailnya…

Tanggapan 2 – Filipus Aron

Dear Pak Robby,

Sebenarnya ada kasus di lapangan dimana pasir yang terproduksi diduga karbonat namun berasal dari reservoir sandstone sehingga saya menanyakan hal ini.
Trims atas bantuannya.

Tanggapan 3 – BSM

Aron,

Untuk batuan klastik, terminologi ‘clay’, ‘silt’, ‘sandstone’, ‘conglomerate’, etc., merupakan klasifikasi berdasarkan dominasi UKURAN BUTIR matriks penyusun batuannya, jadi, tidak dipengaruhi oleh komposisi mineraloginya. Ringkasnya, bisa saja reservoir yg didsikripsi sebagai ‘sandstone’ tsb memiliki komponen penyusun matriks detrital carbonate, nah batupasir / sandstone ini yg secara geologi dinamakan sebagai ‘calcarenite’. Batuan jenis ini biasanya terbentuk tidak jauh2 dari host rock carbonate body, ingat, detrital carbonate tidak bisa ditransport jauh, materialnya sangat rapuh, berbeda dengan kuarsa.
Untuk pertanyaan yg kedua, hmmm, mungkin kawan2 yg berlatarbelakang Reservoir Engineering lebih berkompeten. Tapi, bukankah group-mu justru dr EOR? Secara praktisnya sih kita harus memperhitungkan kekompakan batuan penyusun reservoir, loose sand cenderung lebih problematis, proporsi fine material (silt-clay) dalam matriks (‘fine migration’), perbedaan viskositas antara minyak dan air formasi, jenis pompa yg akan dipasang(semakin besar vibrasinya, akan lebih ‘prone’ terhadap masalah kepasiran), jadinya, lebih banyak experimenting.

Tanggapan 4 – Filipus Aron

Makasih mas Bambang untuk pencerahannya. Maaf baru sempat balas sekarang.
Problem pasir memang cukup menghambat dalam peningkatan produksi terutama ketika sandfacenya telah rusak. Hal ini menyebabkan EOR kurang berfungsi sehingga problem pasir harus diselesaikan dahulu.

Tanggapan 5 – Zein Wijaya

Pak Filipus,

Please find the answer from your questions:

1. Apakah mungkin suatu reservoir sandstone namun memiliki pasir yang ternyata adalah karbonat?

Answer:

Yes, it can be possible..We called this as Carbonate Dune Environment

Please find little bit explaination about this type of Carbonate Environment

Carbonate Dune Environment

Sand dunes composed of carbonate grains are found today in coastal areas where marine carbonate sediments are being deposited and where onshore winds can transport the carbonate sand grains inland to areas of accumulation (McKee and Ward 1983). Although they are most common as linear, elevated ridges forming sea cliffs along the windward shores of tropical islands, carbonate dunes may also form far inland, either from onshore winds or even in continental settings, particularly in arid areas where playa-type sedimentation occurs.

Even though eolian deposits are common today, they have not been reported frequently among ancient carbonate rocks. There may be two reasons for this apparent discrepancy:

• Few geologists have correctly recognized wind-deposited carbonates.

• Because of their exposed coastal setting, these carbonates tend not to be preserved in the rock record.

Among the better-known areas of modern carbonate deposition, carbonate eolianites have been found in the Bahamas, Yucatan, the Persian Gulf, and western Australia. In addition, lithified Pleistocene dunes constitute the dominant land forms in most of such coastal areas. The propensity for such exposed carbonate sands to become cemented rapidly (if incompletely) probably accounts for their common occurrence in Holocene carbonate settings.

Key Depositional Characteristics

No grain type is particularly characteristic of carbonate dunes — the wind transports whatever kinds of sedimentary particles that are available. Accordingly, eolianites may be composed of ooids, pellets, foraminifera, etc. Although a high degree of sorting, rounding, and polish of fine- to medium-size sand grains is characteristic of dune sands, the same may also be said of beach or oolitic-bar sands (which may merge at their upper boundary with coastal dunes). The common presence of terrestrial fossils may be useful indicators: land snails, vertebrate remains, preserved root casts, and molds are especially diagnostic of the eolian environment (Ball 1967).

Sedimentary structures are probably the most reliable indicators of eolian origin (McKee and Ward 1983), especially certain forms of cross-bedding, such as steep, large-scale foreset beds (about 30° and up to about 20 meters long) that dip predominantly landward

2. Bila suatu lapangan mengalami masalah perpasiran, bagaimana rumus untuk menghitung rate produksi minyak maksimal tanpa menyebabkan pasir terproduksi?

For detail explaination and equation that can be used to estimate sand production rate, I will put in file attachment (pdf) because If I write it down the equation in this email, the format will be massed up after you receive the email.

Another thing for your reference, If you can get access to SPE Library (one petro), you can download SPE paper below:

Paper Number 04-588

Title Modeling The Rate Of Sand Production

Authors Fjær, E., Cerasi, P. and Li, L. , SINTEF Petroleum Research; Papamichos, P., Aristotle University of Thessaloniki, Greece, and SINTEF Petroleum Research, Trondheim.
Source Gulf Rocks 2004, the 6th North America Rock Mechanics Symposium (NARMS), June 5 – 9, 2004 , Houston, Texas

This paper gave detail explaination about mathematical model to estimate sand production rate.

Answer:

Particle production occurs in weak sandstone formations. It causes operational problems, such as:

a Production equipment erosion and damage

b Need for removal of polluted sand from rig

Sand production problem is handled through the well completion strategy by implementation of sand control.

a. Active sandcontrol, like gravel pack, screen or consolidation treatment;

b. Passive sand control through drawdown / flow rate / perforation shot density etc.

Sand control usually reduces productivity; active sand control also requires maintenance

(i.e. gravel pack poisoning). Therefore, one needs to predict where, when and to what extent sanding will occur. Notice: Sand production may cause enhanced petroleum production!

The main requirements for sanding to occur are failure of the formation by

shear failure or

tensile failure and mobilisation of the failed rock fragments (particles) by

erosion.

The analysis of shear failure, which is thought to be responsible for massive sand production, is formally similar to that of borehole stability. We consider for simiplicity a vertical well with a permeable wall (otherwise no production). This is an example of open hole production, but the same kind of analysis can be applied to perforation cavities. The pore pressure is higher than the well pressure during production, and the parameter we calculate is the critical drawdown

Hope this answer your question. Good Luck.