Petroleum Engineering UIR

This chapter, entitled “Acidising and other Matrix Treatments”, discusses the chemical methods of well stimulation. The common factor among these treatments is that they are carried out under matrix conditions i.e. the injected fluids flow radially away from the wellbore since the treatment fluid is injected into the well at rates and pressures below that required for creation of a hydraulic fracture. This chapter mainly concentrates on the injection of acid (“Acidising”), the most frequently employed of the chemical treatments.

Matrix (stimulation) treatments are a common form of well intervention aimed at removing this formation damage and restoring the well to its natural, undamaged inflow performance. An alternative stimulation technique - propped hydraulic fracturing - will be covered in a later chapter. This latter well treatment can bypass this damage and/or increase the effective wellbore radius. Either of these stimulation treatments may be carried out immediately after drilling the well is completed or at any time in the well’s producing lifetime when they can be economically justified. Matrix stimulation treatments increase well productivity by pumping a specially formulated treatment fluid (frequently, but not always, an acid) which is designed to remove (normally dissolve) the formation damage. However, the keys to successful treatments are:

1) The identification of a suitable candidate well which is capable of a greater hydrocarbon production rate.

2) The selection of the optimum type of treatment fluid for the removal of the formation damage.

3) The design of the operational aspects of the treatment.

Tuesday, May 24, 2011

Tahap - Tahap Simulasi Reservoir

5/24/2011 01:22:00 PM

Victor Manik

1 comment

Ada ungkapan populer dalam dunia komputer yang menggambarkan pentingnya data dalam suatu simulasi, yaitu "GIGO : garbage in, garbage out". Persiapan data bertujuan untuk mendapatkan data yang valid dan sesuai kebutuhan didasarkan pada tujuan dan prioritas simulasi. Prosentase keakuratan hasil simulasi yang dilakukan, ditentukan oleh validitas data yang dipergunakan, sehingga tanpa data yang memadai gambaran yang diharapkan tidak akan tercipta atau bahkan akan memberikan informasi yang menyesatkan.

Data-data yang dibutuhkan untuk melakukan simulasi dapat diperoleh dari berbagai sumber data yang memungkinkan. Meskipun demikian, sebagian besar dari data tersebut tidak dapat langsung dipakai, tetapi memerlukan proses pengolahan sehingga dihasilkan data yang siap pakai. Pemilihan sumber data serta pengolahan juga sangat berpengaruh terhadap kesiapan data itu sendiri, yang pada alkhirnya juga berpengaruh terhadap hasil simulasi secara keseluruhan.

Monday, May 23, 2011

Cementing

5/23/2011 11:41:00 AM

Victor Manik

Operasi penyemenan merupakan bagian dari operasi pemboran yang memakan biaya yang besar karena peraatan yang digunakan tidak dapat dipakai kembali , karena tertanam dalam dalam sumur untuk seterusnya, seperti centralizer, casing dan scratcher. Penyemenan harus benar-benar sempurna dan tidak terjadi rongga-rongga pada tempat yang disemen sebabkan menyebabkan kerusakan casing akibat mengembangnya udara atau fluida lainnya yang masuk dalam rongga tersebut akibat terkena temperatur dan tekanan yang tinggi. Operasi penyemenan bertingkat (stage cementing) diterapkan apabila : Sumur terlalu dalam, Formasi diatas dan dibawah zona yang disemen cukup kompak dan jauh, dan Untuk menghindari tekanan pompa yang berlebihan, sehingga dapay mengurangi pengeluaran biaya.

Cementing Procedures

5/23/2011 11:32:00 AM

Victor Manik

Penyemenan suatu sumur merupakan salah satu faktor yang tidak kalah pentingnya dalam suatu operasi pemboran. Berhasil atau tidaknya suatu pemboran, salah satu diantaranya adalah tergantung dari berhasil atau tidaknya penyemenan sumur tersebut.

Penyemenan sumur secara integral, merupakan salah satu aspek yang sangat penting dalam suatu operasi pemboran, baik sumur minyak maupun gas. Semen ter-sebut digunakan untuk melekatkan rangkaian pipa selubung dan mengisolasi zona produksi serta mengantisipasi adanya berbagai masalah pemboran.

Perencanaan penyemenan meliputi :

· Perkiraan kondisi sumur (ukuran, tem-peratur, tekanan, dsb.)

· Penilaian terhadap sifat lumpur pem-boran

· Pembuatan suspensi semen (slurry de-sign)

· Teknik penempatan

· Pemilihan peralatan, seperti centralizers, scratchers, dan float equipment

Program perencanaan penyemenan secara tepat, merupakan hal pokok yang akan mendukung suksesnya operasi pemboran.

Pada dasarnya operasi penyemenan bertujuan untuk :

1. Melekatkan pipa selubung pada dinding lubang sumur,

2. Melindungi pipa selubung dari masalah-masalah mekanis sewaktu operasi pem-boran (seperti getaran),

3. Melindungi pipa selubung dari fluida formasi yang bersifat korosi, dan

4. Memisahkan zona yang satu terhadap zona yang lain dibelakang pipa selu-bung.

Friday, May 6, 2011

Well Dynamic Behaviour

5/06/2011 10:46:00 AM

Victor Manik

Keywords: coning, cusping, radial flow, productivity index (PI), skin, acidising, routine

production testing, bottom hole pressure testing, drill stem testing, horizontal wells,

cresting, productivity improvement factor, tubing performance curves, perforating, artificial

lift, gas lift, beam pumps, electrical submersible pumps, hydraulic pumps, well completion,

christmas tree, sand control, gravel packing.

Introduction and CommercialApplication: Section 8.0 considered the dynamic behaviour

in the reservoir, away from the influence of the wells. However, when the fluid flow

comes under the influence of the pressure drop near the wellbore, the displacement

may be altered by the local pressure distribution, giving rise to coning or cusping. These

effects may encourage the production of unwanted fluids (e.g. water or gas instead of

oil), and must be understood so that their negative input can be minimised.

The wells provide the conduit for production from the reservoir to the surface, and are

therefore the key link between the reservoir and surface facilities. The type and number

of wells required for development will dictate the drilling facilities needed, and the

operating pressures of the wells will influence the design of the production facilities.

The application of horizontal or multi-lateral wells may where appropriate greatly reduce

the number of wells required, which in time will have an impact on the cost of

development.

Horizontal or multi-lateral wells can also be used to cost efficiently access remaining oil

in mature fields.

Drill-Stem Testing Methods

5/06/2011 10:27:00 AM

Victor Manik

Drill-stem testing provides a method of temporarily completing a well to determine the productive characteristics of a specific zone. As originally conceived, a drill-stem test provided primarily an indication of formation content. The pressure chart was available, but served mainly to evaluate tool operation. Currently, analysis of pressure data in a properly planned and executed DST can provide, at reasonable cost, good data to help evaluate the productivity of the zone, the completion practices, the extent of formation damage and perhaps the need for stimulation. A drill-stem test provides an estimate of formation properties and wellbore damage. These data may be used to determine the well's flow potential with a regular completion that uses stimulation techniques to remove damage and increase effective wellbore size.

Reservoir characteristics that may be estimated from DST analysis include:

· Average effective permeability. This may be better than core permeability since much greater volume is averaged. Also, effective permeability rather than absolute permeability is obtained.

· Reservoir pressure: Measured, if shut-in time is sufficient, or calculated, if not.

· Wellbore damage: Damage ratio method permits the estimation of what the well should make without damage.

· Barriers, permeability changes, and fluid contacts: These reservoir anomalies affect the slope of the pressure buildup plot. They usually require substantiating data to differentiate one from the other.

· Radius of investigation: An estimate of how far away from the wellbore the DST can "see".

· Depletion: Can be detected if the reservoir is small and the test is properly run.

Tuesday, May 3, 2011

Sandstone Reservoir

5/03/2011 03:53:00 PM

Victor Manik

Introduction

Treatment fluid selection in sandstone formations is highly dependent on the mineralogy of the rock as well as the damage mechanism. Hydrofluoric (HF) acid is typically used to dissolve the damaging silicate particles. Nonacid systems are sometimes used to disperse whole mud and allow it to be produced with the treating fluid. The criteria for selecting the treating fluid are mineralogy, formation damage mechanism, petrophysics and well conditions.

Formation mineralogy

Compatibility and sensitivity

Compatibility of the formation minerals to the various treating fluids and their additives is a significant issue when selecting fluids for acidizing. Compatibility implies that permeability does not decrease when the treating fluid contacts the formation. This concept of compatibility applies especially to sandstones, where potentially damaging reactions may occur.

Compatibility and sensitivity are related concepts. As stated by McLeod (1984), a successful matrix treatment depends on the favorable response of the formation to the treatment fluid. The treating fluid, therefore, must remove existing damage without creating additional damage through interactions with the formation rock or fluids. A formation is sensitive if the reaction between the rock minerals and a given fluid induces damage to the formation.

The sensitivity of a formation to a given fluid includes all the detrimental reactions that can take place when this fluid contacts the rock. These detrimental reactions include the deconsolidation and collapse of the matrix, the release of fines or the formation of precipitates. The precipitation of some damaging compounds cannot be avoided. Treating and overflush fluid stages are sized; so, there is sufficient volume to push potential precipitates deep enough into the reservoir to minimize their effects because of the logarithmic relationships between pressure drop and distance from the wellbore.

Sandstones can be sensitive to acid depending on temperature and mineralogy. Ions of silicon, aluminum, potassium, sodium, magnesium and calcium react with acid and can form precipitates at downhole temperatures, once their solubility product is exceeded. If these precipitates occur in the near wellbore area, they can damage the formation. Sensitivity depends on the overall reactivity of the formation minerals with the acid. Reactivity depends on the structure of the rock and the distribution of minerals within the rock, i.e., the probability of the acid reaching the soluble minerals.

The sensitivity of sandstone will also depend on the permeability of the formation. Lowpermeability sandstones are more sensitive than high-permeability sandstones for a given mineralogy. Acid formulations should be optimized on the basis of a detailed formation evaluation (Davies et al., 1992, Nitters and Hagelaars, 1990).