Integration of Advanced Production and Image Logging in a High GOR Horizontal Well With Assessment of Remedial Actions

8/10/2019 Integration of Advanced Production and Image Logging in a High GOR Horizontal Well With Assessment of Remedi

1/9

SPE 93473

INTEGRATION OF ADVANCED PRODUCTION AND IMAGE LOGGING IN A HIGHGOR HORIZONTAL WELL WITH ASSESSMENT OF REMEDIAL ACTIONSA.A. Al-Fawwaz, H.K. Mubarak, Saudi Aramco and M. Zeybek, Schlumberger Oilfield Services

Copyright 2005, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the 14th

SPE Middle East Oil & Gas Show andConference held in Bahrain International Exhibition Centre, Bahrain, 1215 March 2005.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper

for commercial purposes without the written consent of the Society of Petroleum Engineers isprohibited. Permission to reproduce in print is restricted to an abstract of not more than 300words; illustrations may not be copied. The abstract must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abst ractProduction logging in high GOR horizontal wells still exhibits

difficulties due to multi-phase, complicated flow regimes in

undulating long well bores. Accurate diagnosis of gas entriesis important for the understanding of the well performance,

reservoir dynamics, characterization and if possible, for shut-

off remedial action.

In this paper, a case study is presented in a horizontal well

with high GOR where oil production decreased significantlydue to gas entries. The example horizontal well is located in

Saudi Arabian Lower Cretaceous carbonate reservoir that has

gas cap and relatively weak aquifer. Although the horizontal

well is placed away from the gas cap, increase in GOR wasobserved after two years of production time. Since GOR

increased to over 5000 SCF/STB by then, an integrated

production logging tool was utilized to detect gas entries anddetermine flow profile.

Results showed that the gas entries were detected from the

high sides of the well and the majority of the gas was entering

from the heel section over 500 ft of interval. Gas hold up inthe well bore was determined from gas sensor tool in real time

and pulsed neutron tool, providing high confidence. All thesensors exhibited coherent measurements, yielding confident

and conclusive results for the gas entries. Image logs andpermeability determinations identified the presence of

different facies with high permeability over the interrelated

entry intervals, supporting the calculated flow profile. Theresults, observed difficulties and recommendations are

discussed for improvements. A single well fine grid numerical

reservoir simulation model was also developed to assess

impact of remedial action plans.

IntroductionIt is well known that increased gas production can

significantly reduce well performance and result in decreased

oil production. Generally, an increase in GOR could be due to

a drop in reservoir pressure or a gas breakthrough. Thedetection of gas entry intervals in the case of early increases

in GOR, provides useful information for understanding

reservoir dynamics and optimizing well placement. Formaximum productivity and choosing well trajectories, the

evaluation of well performance is crucial. Production logging

provides not only the detection of unwanted fluids but alsomeasures effective well length that is needed in well testing

evaluation for complete well performance analysis. In

addition, the length and the number of entries provide

information about the characteristics of the intervals

Eventually, the integration with reservoir and geological datayields more accurate characterization.

Conventional production logging tools developed for

vertical wells often do not perform well in horizontal wellsbecause multiphase flow in horizontal sections is highly

segregated1-4

. In addition, logging conditions in barefoo

horizontal wells can be quite harsh. The integrated production

logging tool string was developed in 1995 and severa

examples of oil/water flow in horizontal wells were

published3,5

. Although three phase flow is addressed, there are

only a few examples6,7

of gas/oil or three phase flow. The firs

example7discussed the challenges of the detection of gas entry

intervals and the results could not pinpoint the entry intervals

due to shortage of intervention and the amount of hold up in

the wellbore.

In this paper, a case study of high a GOR horizontal well is

presented. Since the well started producing a high GOR in a

less than a year, the detection of gas entry intervals was the

primary objective. An integrated production logging too

string including new Gas Hold Up Optical Sensor tool wasrun. The results showed the detection of gas and oil entry

intervals with confidence achieving the objectives. The

integration with static data of open hole and image logs

showed coherent results by identifying high and low

permeability facies where the gas entries were observed from

high permeability facie crossing the wellbore. A fine grid

numerical simulation model based on a commercial simulator

was developed to assess remedial action plans.


2/9

2 A.A. AL-FAWWAZ, H.K. MUBARAK, M. ZEYBEK PE

Gas-Liquid Flow and Integrated Production LoggingTool String

It has been known that generally stratified flow regimes2exist

in horizontal wells, flowing oil and water. It is important that

flow regimes, existing during the flow of fluids be understood

for interpretation and measurement accuracy.

Fig. 1 shows the flow regimes in horizontal wells in thepresence of gas-liquid flow. Mostly stratified or wavy

stratified flow regimes are observed when the deviation is 90

degrees or more. However, the stratified flow domain islimited when the deviation is less than 90 degrees. Plug or

slug flow becomes dominant in this deviation, indicating the

complexity of the flow. Considering the small changes in well

deviation and fluctuations in the well performance as well, themeasurements of gas hold up in real time during each pass

would improve the results

An integrated production logging tool string developed for

horizontal wells was given in detail by Lenn et al3. The tool

string consists of Combinable Production Logging Tool,

providing pressure, temperature, in addition to spinners, phase

velocity of oil using a chemical marker, water velocity using

water flow log, hold ups of oil, water and using electrical

probes, three phase hold up using pulsed neutron tool and

caliper measurements to obtain quantitative determination of

flow profiles. To note that stationary phase velocity

measurement of oil is a direct measurement, requiring no

calibration or correlation and is benchmarked in a flowloop4.

Several examples of integrated production logging in

horizontal wells have been published3,5.

In this study, a new shorter production logging tool,providing x-y caliper, spinner and flow imaging in the same

module was utilized along with the mentioned sensors as

shown in Fig 2.

As mentioned above, although gas hold up is measuredwith pulse a neutron tool, it is a one pass measurement and

requires further processing for quantitative values. In the case

of liquid-gas flow regimes, having quantitative gas hold updata, in real time, in each pass provides useful information and

confidence in interpretation. Hence, including a gas hold up

optical sensor tool in the string is considered to be beneficial

in high GOR wells.

Gas Hold up Optical Sensor Tool was developed usingnew optical sensing technology to enable direct detection of

gas in producing wells8. In gas-liquid mixtures, optical signals

reflected by the optical probes vary from liquid to gas values

in a binary manner. This allows the determination of gas hold

up and gas bubble count. Gas detection is achieved using anoptical sensor sensitive to the optical index of the fluid that is

low for liquid and high for gas. Relative bearing and caliper

measurements are included to determine exact positions of the

probes at any time. The details of the tool specifications are

given by Theron et al.8.

Field ExampleThe field example is from a Middle East Lower Cretaceous

carbonate reservoir. The producing intervals are

predominantly limestone, with intervening tight dolomite

streaks. A gas cap overlies the reservoir and weak pressure

support is provided by an aquifer. The reservoir thickness isaround 250 ft. The porosity of the producing zones is roughly

% 30 and the average permeability is around 13 md. The

hydrocarbon is a light oil with an API gravity of 42. Because

of relatively low permeability and the presence of a large gas

cap, field development is planned based on horizontal wells toincrease well productivity and drainage area and minimize gas

cusping and water coning. Based on simulations andexperience, horizontal wells are placed in the oil column with

optimum distance from GOC and WOC to avoid early

breakthrough of gas or water. However, early increases in

GOR or water are observed in certain wells due to

heterogeneities and fractures intersecting the wellbore. Theidentification of unwanted fluid entry intervals has importance

for the understanding of reservoir characterization and

subsequent remedial actions.

In this paper, a high GOR but dry horizontal well with2800 ft horizontal length was considered for the identification

of gas entry intervals.Well History: The subject well was drilled and put in

production in 1998. Although a majority of horizontal well

are completed as barefoot in this field, this well was

completed with 4 liner, perforated over almost the whole

horizontal section. The well was placed 110 ft below the GOC

to optimize production and minimize gas cusping. The welproduced dry oil with solution GOR initially; however, i

gradually showed an increase of GOR after two years o

production. Fig. 3 shows theproduction history of oil ratesand GOR. Furthermore, it showed that the well was producing

high GOR based on flowing well head pressures. Generally, to

keep the ratio of oil to gas rate high, choke size was variedThis type of exercise fine tunes choke size in favor of oil rate

Since the well was producing quite high GOR, it wasnecessary to find out the gas entry intervals. The well

trajectory along with open hole log results and image logs are

shown in Fig. 4. As noticed, the well trajectory goes up at theend. To avoid any gas cusping through this section, the lower

section of the well was not perforated.

Well Logging: Since the well was producing high GOR, anintegrated production logging tool string with an optica

sensor tool was run. This configuration allowed both real time

gas and water hold up determination. Pulsed neutron three

phase hold up was recorded as an independent measurement toverify and increase the confidence in oil, water and gas hold

ups. The trajectory and the production history suggested tha

only low sides of the wellbore would have some stagnanwater. To obtain flow rates of oil and gas, hold up and velocity

data are required. As planned, flowing passes were conductedfirst, followed by shut-in passes after 4.5 hours of shut-in.

As shown in Fig. 2, the tool string with gas sensor too

was run using 2 coil tubing. Prior to the job, tool accessibilityin the wellbore was assessed via simulation and a dummy run

During the job, no difficulties were encountered in reaching

TD. The distributions of fluids and hold up were establishedduring the passes. Real time optical gas sensor hold up results


3/9

SPE IMPROVEMENTS IN THE DETECTION OF GAS ENTRY INTERVALS WITH INTEGRATED LOGGING IN HIGH GOR HORIZONTAL WELL 3

were obtained in the second run due to difficulties, observing

lack of response in horizontal section in the first run. Electrical

flow imaging sensors identified the presence of a smallamount of stationary water in the deepest low side of the well.

In addition to optical and electrical probes, pulsed neutron

borehole sigma and inelastic far/near ratio provided hold up

information in real time. Bore hole sigma supported the

presence of stationary water with the high value of sigmareading. Although optical and electrical probe hold up outputs

are direct and quantitative, bore hole sigma and inelastic ratiocan be used based on individual phase values. Because the

probe locations are known, flow image output yields the flow

distribution along the wellbore. After establishing the fluid

flow distribution and hold up data, all the sensors were utilized

appropriately. However, pulsed neutron three phase hold upoutput provided quantitative three phase hold up data in

computing center. Both in-line (smaller) and full bore

spinners were also included in the tool string. Since the flow

regime is often segregated in horizontal wells, the spinner canbe used when it is completely immersed in one phase. After

obtaining quantitative hold up data, using well bore size andspinner size, whether the spinner is immersed in one or two

phases can be determined. For example, minimum 70 % of

hold up for lighter fluid would allow an in-line smaller spinner

to be completely immersed in a lighter phase in a 4 ID

completion. In other words, if the hold up for heavier phase is

more than % 30, then the spinner would be immersed in twophases. In that case, the spinner velocity corresponds to

neither phase, assuming flow is segregated, hence phases can

have quite different velocities. It requires % 88 hold up forthe fullbore spinner to be immersed totally in the lighter

phase.

As mentioned in the previous section, oil velocitymeasurements were obtained using a phase velocity log where

oil miscible marker is ejected and detected by pulse neutrontool. In this job, high quality PVL measurements were

obtained to get an oil profile.

In high GOR wells, temperature data could be quite usefulto increase confidence for the identification of gas entry

intervals, especially in the case of the first entry and

significant amount of entry from one interval. Fig. 5shows theflowing and shut-in temperature measurements supporting the

entry intervals with the drop in temperature.

Results and Discuss ionAfter running the first flowing pass, it was identified that gas

was occupying almost % 80 (hold up) of the well bore in the

first 700 feet of the horizontal section. Then gradually, gashold up decreased and correlated with the deviation (Fig. 6).

Gas hold up increased as the well deviation became greaterthan 90 degrees. During shut-in, the fluids segregated as

expected. Using the end points of inelastic ratio, hold up

distribution was obtained as shown in Fig. 6. Bore hole sigmaalso correlated well with gas and oil presence. As expected,

gas was trapped in the high sides of the wellbore.

As mentioned above, spinner data can be used todetermine the velocity of gas wherever the gas hold up is % 70

or greater. The gas flow profile is given in Fig. 6, indicating

major gasentry (almost 80% of the total gas entry) occurrence

interval along the high side of the well, close to the heelOpen hole and image logs suggest that this interval is a

different facie which was also confirmed by log derived

permeability. A second entry was identified from the second

high side of the well where the well goes up again and crosses

into the high permeability facies. Minor gas entry was alsodetected from the toe section. Although different facies were

observed in image logs, the quantitative impact on flow profilecould not be predicted. In fact, the results of the integrated

production logs are now providing more confident reservoi

characterization information. Gas entries from higher

permeability facie indicated that gas is cusping down from

these intervals as schematically shown in Fig. 7.Generally, very small temperature variations are expected

and seen in horizontal wells. However, in this well, the first

entry and subsequently significant amount of gas entries

caused differentiable temperature cooling as shown in Fig. 5supporting the above findings.

It should be noted that oil hold up distribution did noallow to the determination of the oil velocity with spinner due

to low hold up to oil. Hence, the oil velocity could be obtained

only with a phase velocity log. Fig 8. shows examples of a

phase velocity measuring 120 ft/min translating to around 900

bbl/d using oil hold up. The oil flow profile is shown in Fig. 6

indicating almost half of the oil production is coming from thehigh permeability interval in the upper section of the well.

RecommendationsProduction logging in high GOR horizontal wells has been

challenging because of the difficulty in obtaining quantitative

results. Integrated production logging provides quantitativeanswers; however, further improvements would allow more

quantitative results under different scenarios. Although thehold up data is obtained confidently with different sensors, ga

velocity measurements in different scenarios (with hold up

variation) are challenging to obtain quantitatively. Two opticagas sensor tools provide more accurate hold up data with more

coverage of the wellbore. In addition, direct measurement of

gas velocity via gas slugs can be obtained. As indicated in theGas-Liquid flow section, slug or plug flow is obtained when

the deviation is less than 90 degrees. The measurement i

based on cross correlation between two gas hold up optica

sensors when it is applicable for further improvementsSpinner data is to be utilized whenever the spinner i

immersed. In the case of high flow rates in small completions

spinners have limitations. In those cases, flow rates should bereduced to avoid exceeding the limitations. In fact, in this job

the well had to be choked down after observing highvelocities.

Numerical Simulations for Shut Off ConsiderationsIn order to assess the impact of remedial action plans on well

performance by shutting off the gas entry intervals, a fine

gridded single well numerical simulation model was set upbased on a commercial reservoir simulator. A single wel


4/9


model using pebi gridding was used for efficient grid size

optimization as shown in Fig. 9. A total of 35000 grid cells

were used in the segmented simulation area with the actualwell trajectory. Openhole and image logs suggested that the

well was crossing two zones along the trajectory. The model

included two permeability zones as shown in Fig. 9. To

benchmark the model, production log entries, pressure surveys

and observed GOR data were reasonably honored for thehistory. Fig. 10 shows thecomparison of measured GOR (red

dots) and simulation GOR (purple curve). Fig. 11 shows thegas saturation distribution from a numerical simulation

indicating gas entry intervals (flow from intervals) that agrees

well with integrated production logging results. Results

showed that three pressure surveys after 2, 18 and 52 months

were within less than 5 psi of the measured ones.Since the gas entries were observed from the high sides

(high permeability) of the wellbore, shut off is considered for

those intervals. Because the well is shut-in for long periods of

time, the complete history was included in the simulations. Ithas been observed that gas did not recede to original GOC

over more than a one and a half year period.Two scenarios are initially considered in the simulations.

The first scenario considers the shutting off all the high side

(gas entry intervals). In other words, the well is allowed to

produce only from the low permeability intervals (around %

35 of the completion open). Simulations, conditioning to the

optimized bottom hole pressures (reduced oil rate) showedthat GOR can be kept to a low value (very close to solution

GOR) for a long period of time, however, no additional oil

production can be obtained compared to existing oil rate.In the second scenario, shut off is considered for the long

entry interval in the heel section due to practical

considerations. In this case, % 65 of the completions are open.The results showed that GOR gradually increases to 2000

scf/stb over six years under optimized pressure with a similaroil rate to the first scenario. Fig. 12 shows numerical

simulation of gas saturation after shut off.

Alternatively, a sidetrack option (30 ft deeper) wasevaluated as shown in Fig. 13. Fig. 14shows the production

history with the existing well and the production prediction

with the sidetrack well. Simulation results indicate that thesidetrack well production oil rate of 1250-2000 stb/d with

solution GOR for the next six years.

ConclusionsIn this paper, a case study is presented in a horizontal well

with high GOR where oil production decreased significantlydue to gas entries.

It has been shown that integrated production logging canbe used to diagnose gas entries in high GOR horizontal wells.

The integration of diagnostic flow profiles, gas entryintervals and well evaluation can yield important information

on reservoir characterization and dynamics. In fact, the case

history of this well revealed that the impact of the gasbreakthrough could not be confidently predicted based on

static data alone. The identification of entry intervals and

relation to certain facies can be helpful for future wel

placement practices.Numerical simulations supported the entry intervals. Shu

off considerations of the high side of the wellbore sections

suggested that GOR can be minimized; however no significan

increase in oil production can be obtained. As an alternative, a

sidetrack well option was also considered. In fact, productionpredictions yielded increased oil production with no free gas.

Acknowledgments

We thank Saudi Arabian Oil Company (Saudi Aramco) forpermission to publish this paper. We also like to thank to Mr

Salam P. Salamy for his discussions and inputs.

Nomenclature

GOR: Gas Oil Ratio, scf/stb

PVL: Phase Velocity Log

WOC: Water Oil Contact

References1. Kuchuk, F.J., Lenn, C., Hook, P., and Fjerstad, P.

Performance Evaluation of Horizontal Wells, SPE39749 presented at the SPE Asia Pacific Conference on

Integrated Modeling for Asset Management, Kuala

Lumpur, Malaysia, 2324 March 1998.2. Lenn, C., Kuchuk, F.J., Rounce, J., and Hook, P.

Horizontal Well Performance Evaluation and Fluid Entry

Mechanisms, SPE 49089 presented at the SPE Annual

Technical Conference and Exhibition, New Orleans, LA

2730 Sept. 1998.3. Lenn C., Bamforth S. and Jariwala H.: Flow Diagnosis

in an Extended Reach Well at the BP Wytch FarmOilfield Using a New Toolstring CombinationIncorporating Novel Production Logging Technology,

SPE 36580 presented at the 1996 SPE Annual Technica

Conference and Exhibition, Denver, Colorado, 6-9 Oct.4. Roscoe, B. and Lenn, C.: Oil and Water Flow Rate

Logging in Horizontal Wells Using Chemical Markers

and a Pulsed-Neutron Tool, SPE 36230 presented at the

7th Abu Dhabi International Petroleum Exhibition and

Conference, Abu Dhabi, U.A.E., 13-16 October, 1996.

5. Middle East Well Evaluation Review, Schlumberger p.2229 v19, 1997.

6. Frankenburg, A., Bartel, P., Roberts, G. and Hupp, DGas Shutoff Evaluation and Implementation, NorthSlope Alaska, SPE 62892 presented at the SPE Annua

Technical Conference and Exhibition, Dallas, TX, 14

Oct. 2000.7. Al-Ali, H. A., Salamy S.P. and Haq, S.A.: The

Challenges of Detecting Gas Entries in Horizontal Wel

by Using Integrated Production Logging Tool, Case

Study, SPE 65528 presented at 12th Middle East Oi

Show, Bahrain, 17-20 March, 2001.


5/9


8. Theron, B., Vuhoang, D., Rezgui, F., Gatala, G.,McKeon, D. and Silipino, L.: Improved Determination

of Gas Hold up Using Optical Fiber Sensors, SPLWA2000.

8. Theron, B., Vuhoang, D., Rezgui, F., Gatala, G.,McKeon, D. and Silipino, L.: Improved Determination

of Gas Hold up Using Optical Fiber Sensors, SPLWA2000.

Figure 1 - Gas-Liquid Flow regimes

Figure 2 - Shorter Tool String including opti cal gas sensor

Figure 3 - Production histor y (GOR shown with r ed dots)


6/9

Figure 4 - Well t rajectory wi th open ho le and FMI dataFigure 4 - Well t rajectory wi th open ho le and FMI data

Figure 5 - Temperature during f lowing shut-in


7/9


Permeability

Figure 6 - Integrated Advanced Producti on Loggi ng results.Figure 6 - Integrated Advanced Producti on Loggi ng results.

Figure 7 - Schematic drawings of the Flagship results Figure 8 - Oil velocity measurement using phase velocity.

Ejection Detection


8/9


Figure 9 - Pebi Gridding and well cross section in numericalmodel

Figure 10. History match of GOR

Figure 11 - Numerical simulation: gas breaking through

Figure 12 - Numerical simulation: gas saturation after shut of f theheel section with major gas entry

Figure 13 - Alternative option of deeper side track well


9/9


Figure 14 - Production prediction with sidetrack well

Documents

Integration of Advanced Production and Image Logging in a High GOR Horizontal Well With Assessment of Remedial Actions