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Summary The combination of pressure-transient and production-log (PL) analyses has proved valuable in characterizing reservoir flow behavior in the giant Tengiz field. Among the important findings is the absence of clear dual-porosity flow. This observation contra- dicts an earlier interpretation that the reservoir contains a well- connected, natural fracture network. Fracturing and other secondary porosity mechanisms play a role in enhancing matrix permeability, but their impact is insufficient to cause dual-porosity flow behavior to develop. Flow profiles measured with production logs consistently show several thin (10 to 30 ft) zones dominating well deliverability over the thick (up to 1,040 ft) perforation intervals at Tengiz. A comparison of PL results and core descriptions reveals a good correlation between high deliverability zones and probable expo- sure surfaces in the carbonate reservoir. Contrary to earlier postulations, results obtained from pressure- transient and PL data at Tengiz do not support rate-sensitive productivity indices (PI’s). Inclusion of rate variations in reconciling buildup and drawdown test results addressed this issue. We developed wellbore hydraulic models and calibrated them with PL data for extending PI results to wells that do not have measured values. A simplified equation-of-state (EOS) fluid description was an important component of the models because the available black-oil fluid correlations do not provide reliable results for the 47°API volatile Tengiz oil. Clear trends in reservoir quality emerge from the PI results. Introduction A plethora of publications exists on transient testing. However, only a few papers address the issue of combining multidisciplinary data to understand reservoir flow behavior (Refs. 1 through 4 are worthy of note). We used a synergistic approach by combining geology, petrophysics, transient tests, PL’s, and wellbore-flow modeling to characterize the reservoir flow behavior in the Tengiz field. Understanding this flow behavior is crucial to formulating guidelines for reservoir management. Permeability estimation from pressure-transient data is sensi- tive to the effective reservoir thickness contributing to flow. Unfortunately, difficulties associated with the calibration of old openhole logs, sparse core coverage, and a major diagenetic over- print of solid bitumen combine to limit the identification of an effective reservoir at Tengiz based on openhole log data alone. Consequently, PL’s have been used to identify an effective reser- voir in terms of its flow potential. A limitation of production logs is that they only measure fluid entering the wellbore and are not necessarily indicative of flow in the reservoir away from the well. Pressure data from buildup and drawdown tests, on the other hand, provide insights into flow behavior both near the well and farther into the reservoir. The combination of pressure-transient analysis using simultaneous downhole pressure and flow-rate data along with measured production profiles provides an opportunity to reconcile near-wellbore and in-situ flow behavior. Expansion of reservoir fluids along with formation compaction provides the current drive mechanism at Tengiz because the reser- voir is undersaturated by over 8,000 psia. As the field is produced, reservoir stresses will increase in response to pressure decreases. 5 Increased stresses can significantly reduce permeability if natural fractures provide the primary flow capacity in the reservoir. Wells producing at high drawdowns provide an opportunity to investigate the pressure sensitivity of fractures within the near-wellbore region. Early interpretations of pressure-transient tests at Tengiz uncovered a significant discrepancy between buildup and draw- down permeability, despite efforts to carefully control flow rates during the tests. Drawdown permeabilities typically exceeded the buildup results by 20 to 50%. Although this finding appears coun- terintuitive to the expectation that drawdowns (that is, higher stresses) would lead to lower permeability, it indicated a possible stress dependence on well deliverability. The method proposed by Kabir 6 to reconcile differences between drawdown and buildup results proved useful in addressing this issue. The opportunities to collect PL and downhole pressure data at Tengiz are limited by mechanical conditions in some wells and by the requirement to meet the processing capacity of the oil and gas plant. On the other hand, accurate wellhead-pressure and flow-rate data are routinely available. Wellbore hydraulic calculations pro- vide a basis for calculating flowing bottomhole pressures (FBHP’s) with the available surface data. Calculated FBHP’s can be com- bined with available reservoir pressure data to determine PI’s for wells lacking bottomhole measurements. The ability to compute accurate fluid properties is critical in applying this approach. Unfortunately, the black-oil correlations routinely used in wellbore hydraulic calculations 7–9 do not provide reliable results for the volatile Tengiz oil. We obtained good agree- ment between laboratory measurements of fluid properties and cal- culated values using a simplified EOS. 10 Surface and bottomhole data collected during PL operations provide a basis for validating wellbore hydraulic calculations. Networks of natural fractures can dominate the producing behavior of carbonate reservoirs such as Tengiz. Early identifica- tion of fractured reservoir behavior is critical to the successful development of these types of reservoirs. 11 We present an approach for resolving reservoir flow behavior by combining production profiles, pressure-transient tests, and wellbore hydraulic calcula- tions. Furthermore, we discuss the PL procedures developed to allow acquisition of the data required for all three types of analy- ses in a single logging run. Field examples from Tengiz highlight the usefulness of this approach. Background The Tengiz field is located on the south side of the Pri-Caspian basin. It is one of several large carbonate banks found at various depths all around the edge of the basin, as shown in Fig. 1. The platform evolved during Devonian and Carboniferous time by recurrent deposition of skeletal fragments and lime mud. Fig. 2 shows that the top of the central, or platform, portion of the reser- voir is relatively flat with localized structural highs on the northern and eastern edges. The platform is bounded by faults or lithologic Characterization of a Carbonate Reservoir With Pressure-Transient Tests and Production Logs: Tengiz Field, Kazakhstan K.T. Chambers,* SPE, and W.S. Hallager,** SPE, Tengizchevroil; C.S. Kabir, SPE, Chevron Overseas Petroleum Technology Co.; and R.A. Garber, Chevron Petroleum Technology Co. **Now with Chevron Petroleum Technology Co. **Now with Chevron Canada Resources Copyright © 2001 Society of Petroleum Engineers This paper (SPE 72598) was revised for publication from paper SPE 38657, first presented at the 1997 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 5–8 October. Original manuscript received for review 2 December 1997. Revised manu- script received 2 January 2001. Paper peer approved 20 June 2001. 250 August 2001 SPE Reservoir Evaluation & Engineering

Sonnet 18 PDF

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© Gyldendal, 2012 1

Sonnet 18 By William Shakespeare

Pre-reading

1. Vocabulary

a. Change the meaning of the words by adding a prefix.

Prefix Prefix

perfection certainty

changing typical

permanence transient

mortality constant

relaxed

Learning check

In pairs: student A reads out the words without prefix and student B, without looking at the task,

has to add prefixes to the words.

b. Match words that mean (almost) the same.

unchanging fleeting enduring alter

change eternal

constant transient

c. Turn the following words into nouns.

Noun Noun

immortal permanent

eternal constant

perfect alter

Learning check b. and c.

In pairs: student B reads out the words in the left columns, and student A, without looking at the

tasks, has to come up with the corresponding synonyms and nouns.

Page 2: Sonnet 18 PDF

© Gyldendal, 2012 2

Post-reading LEARNING CHECK

No study aids.

What do you remember?

a) With what does the speaker compare the lover? _________________________________

b) How is the lover going to live eternally? ______________________________________

Text-related assignment

1. Written assignment: Write YOUR OWN sonnet. You may either compose it independently or use one of the templates below.

You must write in iambic pentameter.

There must be a systematic rhyme scheme.

Take advantage of the possibilities given by the structure (quatrains/octave, tercets/sestet,

couplet) when you develop your ideas through the poem.

You must NOT use the word love in the text, but love may be the theme.

Shall I compare a

You are b

a

And b

Sometimes, c

And often d

And every c

By d

But e

Nor f

Nor e

When f

So long g

So long g

Let me not a

Admit impediments b

a

b

O no, c

It is d

c

d

I e

f

e

f

If this g

I g

Wider contexts

1. Critical context: agreement with James Boyd-White.

Not everyone is willing to accept the role of Sonnet 18 as the ultimate English love poem. The

British critic James Boyd-White, for example, argues that the poem is in fact not a love poem at

all as we hear nothing about the beloved. He sees the poem as a self-glorification of the poet:

“What kind of love does 'this' in fact give to 'thee'? We know nothing of the beloved’s form or

height or hair or eyes or bearing, nothing of her character or mind, nothing of her at all, really.

Page 3: Sonnet 18 PDF

© Gyldendal, 2012 3

This 'love poem' is actually written not in praise of the beloved, as it seems, but in praise of

itself. Death shall not brag, says the poet; the poet shall brag. This famous sonnet is in this view

one long exercise in self-glorification, not a love poem at all; surely not suitable for earnest

recitation at a wedding or anniversary party, or in a Valentine.”

James Boyd-White; “The Desire for Meaning in Law and Literature” in Current Legal Problems

2000, vol. 53, p. 142

Do you agree with this view of the poem? Why/why not?

2. Literary Context: other work by the same author: ”Sonnet 73”

Compare sonnet 18 and sonnet 73 with special reference to what each of these sonnets has to say

about love and age.

SONNET 73

That time of year thou mayst in me behold

When yellow leaves, or none, or few, do hang

Upon those boughs which shake against the cold,

Bare ruin'd choirs, where late the sweet birds sang.

In me thou seest the twilight of such day

As after sunset fadeth in the west,

Which by and by black night doth take away,

Death's second self, that seals up all in rest.

In me thou see'st the glowing of such fire

That on the ashes of his youth doth lie,

As the death-bed whereon it must expire

Consumed with that which it was nourish'd by.

This thou perceivest, which makes thy love more strong,

To love that well which thou must leave ere long.

Glossary

behold se

bough gren

ruined choirs dele af kirke,

som ligger i ruiner

expire uddø

consume fortære, be

nourished: blive næret

perceive sanse, erkende

ere before