Well development

Fig. 3.24 shows the cost breakdown of a typical development well. As can be seen, drilling operations are the area with the largest scope for cost savings. The actual costs of a well show considerable variations and are dependent on a number of factors, e.g. ... 

Figure 3.24 Cost break down for a development well...

It is important to realise that knowledge of depositional processes and features in a given reservoir will be vital for the correct siting of the optimum number of appraisal and development wells, the sizing of facilities and the definition of a reservoir management policy. 

Carbonate rocks are more frequently fractured than sandstones. In many cases open fractures in carbonate reservoirs provide high porosity / high permeability path ways for hydrocarbon production. The fractures will be continuously re-charged from the tight (low permeable) rock matrix. During field development, wells need to be planned to intersect as many natural fractures as possible, e.g. by drilling horizontal wells. 

It is clear that if the area - depth method had been applied to the above example, it would have led to a gross over-estimation of STOMP. It would also have been impossible to target the best developed reservoir area with the next development well. 

If no appraisal was performed, and the development was started based, say, on the medium case STOMP of 48 MMstb, then the actual STOMP would not be found until the facilities were built and the early development wells were drilled. If it turned out that the STOMP was only 20 MMstb, then the project would lose 40 million, because the facilities were oversized. If the STOMP is actually 48 MMstb, then the NPV is assumed to be the same as for the medium case after appraisal. If the STOMP was actually 100 MMstb, then the NPV of + 40 million is lower than for the case after appraisal (+ 66 million) since the facilities are too small to handle the extra production potential. 

The type of development, type and number of development wells, recovery factor and production profile are all inter-linked. Their dependency may be estimated using the above approach, but lends itself to the techniques of reservoir simulation introduced in Section 8.4. There is never an obvious single development plan for a field, and the optimum plan also involves the cost of the surface facilities required. The decision as to which development plan is the best is usually based on the economic criterion of profitability. Figure 9.1 represents a series of calculations, aimed at determining the optimum development plan (the one with the highest net present value, as defined in Section 13). 

If the original field development plan was not based on a 3-D seismic survey (which would be a commonly used tool for new fields nowadays), then it would now be normal practice to shoot a 3-D survey for development purposes. The survey would help to provide definition of the reservoir structure and continuity (faulting and the extension of reservoir sands), which is used to better locate the development wells. In some cases time-lapse 3-D seismic 4D surveys carried out a number of years apart, see Section 2) is used to track the displacement of fluids in the reservoir. 

The data gathered from the logs and cores of the development wells are used to refine the correlation, and better understand areal and vertical changes in the reservoir quality. Core material may also be used to support log data in determining the residual hydrocarbon saturation left behind in a swept zone (e.g. the residual oil saturation to water flooding). 

Fluid samples will be taken using downhole sample bombs or the MDT tool in selected development wells to confirm the PVT properties assumed in the development plan, and to check for areal and vertical variations in the reservoir. In long hydrocarbon columns (say 1000 ft) it is common to observe vertical variation of fluid properties due to gravity segregation. 

Reservoir pressure is measured in selected wells using either permanent or nonpermanent bottom hole pressure gauges or wireline tools in new wells (RFT, MDT, see Section 5.3.5) to determine the profile of the pressure depletion in the reservoir. The pressures indicate the continuity of the reservoir, and the connectivity of sand layers and are used in material balance calculations and in the reservoir simulation model to confirm the volume of the fluids in the reservoir and the natural influx of water from the aquifer. The following example shows an RFT pressure plot from a development well in a field which has been producing for some time. 

New technology is applied to existing fields to enhance production. For example, horizontal development wells have been drilled in many mature fields to recover remaining oil, especially where the remaining oil is present in thin oil columns after the gas cap and/or aquifer have swept most of the oil. Lately, the advent of multi-lateral wells drilled with coiled tubing have provided a low cost option to produce remaining oil as well as low productivity reservoirs. 

Due to such subtleties, the need to develop well-defined basic events, failure modes, and equipment boundaries prior to data encoding cannot be overemphasized. Familiarity with failure definitions and failure severities will be extremely helpful to the analyst. Figures 2.1 and 2.2, reprinted from IEEE Std. 500-19845, list a large number of failure modes by failure severity and may help encode failures. IPRDS also contains helpful information on failure encoding. Information on some equipment boundaries may be found in the Data Tables in Section 5.5. 

Figure 4-286. LWD logs recorded while drilling in a development well. Courtesy Anadrill [113].)...

Production well, exploitation well, development well 0... 

A development well is a well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive. 

If the well is completed for production it is classified as an oil or gas development well. If the well is not completed for production, it is classified as a dry development hole. 

Development Extension well QO (Step-out well) Development well Q (Production well) Service well 0 (Injection well, observation well, disposal well, etc.) Wells for production purposes - Production well 0 - Injection well 0 - Production- OO injection well - Appraisal well O - Piezometric well Special wells Disposal well O Absorptive well O Development well OOO Service well 0 Miscellaneous wells Appraisal well 00 (Extension well) Production well 0 (Exploitation well)... 

Development Development well OO Development well OO Exploration well O Auxiliary well O Production well O - oil - gas Injection well O - water - gas - in-situ combustion Appraisal well OO Development well O... 

Development Development well Q Development well 0 Service well 0 Development 0O0 well Service well 0 Development well - Development 0 test well - Development well0 - Injection well 0 - Observation well 0 Special well - Disposal well 0 - Storage well, etc. 0 Development well 0 Injection well 0... 

The few exceptions to this general rule arise when the a-carbon carries a substituent that can stabilize carbonium-ion development well, such as oxygen or sulphur. For example, 1-trimethylsilyl trimethylsilyl enol ethers give products (72) derived from electrophilic attack at the /J-carbon, and the vinylsilane (1) reacts with a/3-unsaturated acid chlorides in a Nazarov cyclization (13) to give cyclopentenones such as (2) the isomeric vinylsilane (3), in which the directing effects are additive, gives the cyclopentenone (4) ... 

Many theoretical embellishments have been made to the basic model of pore diffusion as presented here. Effectiveness factors have been derived for reaction orders other than first and for Hougen and Watson kinetics. These require a numerical solution of Equation (10.3). Shape and tortuosity factors have been introduced to treat pores that have geometries other than the idealized cylinders considered here. The Knudsen diffusivity or a combination of Knudsen and bulk diffusivities has been used for very small pores. While these studies have theoretical importance and may help explain some observations, they are not yet developed well enough for predictive use. Our knowledge of the internal structure of a porous catalyst is still rather rudimentary and imposes a basic limitation on theoretical predictions. We will give a brief account of Knudsen diffusion. 

T Temperature WDWN Well-developed, well-nourished... 

The Lewis acidity and reactivity of these alkyl aluminum cocatalysts and activators with Lewis basic polar monomers such as acrylates make them impractical components in the copolymerization of ethylene with acrylates. To address this shortcoming, Brookhart et al. developed well-defined cationic species such as that shown in Fig. 2, in which the counterion (not illustrated) was the now-ubiquitous fluorinated arylborate family [34] such as tetrakis(pentaflurophenyl)borate. At very low methyl acrylate levels the nickel catalysts gave linear copolymers but with near-zero levels of acrylate incorporation. 

The technology of component-based systems is becoming fairly well established not so the methods to develop them. To be successful, serious enterprise-level development needs clear, repeatable procedures and techniques for development, well-defined and standard architectures, and unambiguous notations whereby colleagues can communicate about their designs. 

When comparing these results with those previously obtained using carbohydrate-based vinyl ethers as chiral dienophiles, this improved facial diastereoselectivity to heterodienes under similar conditions is noteworthy.81 The efficient chiral transfer in the second example might mostly be attributed to the specific architecture of the l,2 5,6-di-0-isopropylidene-a-D-glucofuranose moiety.Those findings open the way to develop well-defined spiro-carbohydrate templates towards improved auxiliaries for chirality transfer in a wide range of syntheses. 

Highly promising nanofillers, nanoclays and carbon nanotubes are also developing well. Depending on the reinforcement, the main difficulties are ... 

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