Production Logging Definition

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D . DEFINITION OF PRODUCTIONLOGGING

D . 1 DEFINITION OF PRODUCTIONLOGGING

Production logging is the measurement of fluidparameters on a zone-by-zone basis to yieldinformation about the type and movement offluids within and near the wellbore.

Production logging is intended primarily formeasuring the performance of producingwells. It provides diagnostic information, pin-points where fluids such as water, oil and gasare entering a well and gives an indicationabout the efficiency of the perforations.

Traditional production logging involves fourmeasurements - flow, density, temperature andpressure. However, only the flow and densityreadings are used in traditional quantitativeproduction logging analysis. Temperature andpressure data have normally been used in aqualitative way to compute in-situ flow prop-erties and locate zones of entry of fluid into awell.

D . 2 HISTORY OF PRODUCTIONLOGGING

Modern Production Logging is far from theearly beginnings of the technique, with highlyaccurate sensors all on a single tool with si-multaneous acquisition. However a lot of sen-sors go back some considerable time. Tem-perature surveys were first used in the mid1930s. One use was the estimation of the topof the cement behind the casing. The settingprocess of the cement is an exothermic reac-tion, it gives off heat. Hence the temperaturesensor sees where there is cement in thewell. (Note; this method is still used, in orderto work well the log has to be run less than 12

hours after the cement has been pumped.)

By the late 1950s and early 1960s the basicsensor types had been developed as individualtools. The surveys required a seperate pass toobtain flowmeter, gradiomanometer, tempera-ture and so on. 1970 saw the sensors packagedtogether in one tool, meaning a more efficient

single run in the hole. The individual meas-urements still had to be run one at a time. Bythe end of the decade advances in electronicsallowed everything to be recorded in a singlepass across the zone of interest. This had manyadvantages not least the savings in time.

Improvements continued through the 1980s tothe present day with better sensors, especiallypressure gauges, and deployment methods.The latest tool uses completely new technologyto measure a flow profile for the individual

fluid phases all around the borehole.

D . 3 USES OF PRODUCTIONLOGGING

Production Logging is put to many uses de-pending on the reservoir type, well conditionsand the perceived problem. (See Figure D1).Some of the major ones are:

1. Evaluate completion performance- New wells- Injection wells- Re-completions

2. Monitor reservoir performance & variations- Flow profile- Well test- Completion Efficiency

3. Diagnose well problems- Water entry- Gas entry- Leaks and mechanical

problems- Flow behind casing

4. Other- Guidance for workover- Information for enhanced oil

recovery projects- Identify boundaries for field

development


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CasingLeak

TubingLeak

Packer

Leak

P1

P2

P2>>P1

Bad Cement

o i l

Unwantedfluid flow

Fig. D1: Common problems encountered in the producing wells.

Some are due to mechanical problems others to the reservoirs


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D . 4 PRODUCTION LOGGINGMEASUREMENTS

D .4 . 1 ToolsProduction logging tools consist of a numberof sensors which make the measurements in-side the well (Figure D2). The main types are:

1. Flowrate (fluid velocity) measurement- Spinner rotation

2. Fluid density measurement- Differential pressure- Gamma ray attentuation

3. Well bore temperature- Variance in resistance

4. Well bore pressure- Strain gauges- Crystal gauges

A number of auxiliary measurements are usedto augment or assist in the analysis of the ma-

jor logs. They are:

- GR /CCL for correlation- Caliper (mechanical)

- Fluid sampling- Noise Logs- Tracer surveys- Water Flow Log

Flowmeter

Fig. D2: A typical production logging tool string con-tains a number of sensors


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D. 4. 2 Applications of specificmeasurements

Each sensor has some specific uses, most areutilised in combination, however, to give a to-tal answer for the well/reservoir.

1. Flowmeter- Determine producing zones- Stimulation evaluation- Secondary recovery- Flow potential evaluation (SIP,

AOF)

2. Temperature- Location of production or injection

zones

- Monitor frac performance- Gas entry- Fluid movement behind pipe- Fluid conversions

3. Fluid Density- Determine volumetric flow in two

phase flow- Show entry points in three phase

flow

4. Pressure

- Well test analysis (kh, skin)- Reservoir extent, boundaries- Fluid conversions- AOF, SIP determination

Up

Run

Down

Run

Gradio

Temperature

Perforations

800

700

600

Spinners

Fig. D3: A typical production log.

D . 5 PRODUCTION LOGGINGENVIRONMENT

The production logging environment is verydifferent from that of open hole logging.Firstly in place there is normally a completion,which can take many forms. The reservoirzone may be open hole, perforated casing orgravel pack. There may be single or multiplezones and single or multiple tubings.

The log is normally run in dynamic conditions,the well is flowing mixtures of liquids andgases.

- Oil, water, polymers.- Methane +, N2, CO2, H2S, He.

(Quite often there are solids present - forma-tion, frac propant, paraffin, scale, diverterballs, etc.)

Hence care and attention has to be taken in thelogging program so that the maximum infor-mation is obtained to answer the problem.


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D . 6 LOGGING AND INTERPRETA-TION PROCEDURES

The procedure to ensure a successful produc-

tion log is simple and can be broken down intothree steps,

- programming the job,- running the job and- interpreting the data.

D. 6. 1 Programming the jobThe first step starts with defining the problem:

e.g. Oil production is falling, water cutis increasing.

Then list and quantify symptoms and wellconditions, for example:

Water Cut has increased from 2% to15% in six months

Total production has fallen from 800 to500 B/D

GOR - 350 cu ft/bbl

Tubing head pressure - 1200 psia

Oil gravity - 30 oAPI

Gas gravity - 0.7

Then define sensors needed and technique nec-essary to gather required data. (Mechanicalconfiguration of the well must be considered.)This may include:

Fluid velocity, density, pressure, andtemperature need to be measured

Data is to be taken vs depth and vs timewith the well flowing and static

5 1/2-in. casing set to 9550 ft. 0 devia-tion

2 7/8-in. tubing set to 9350 ft.

Perforations - 9400-9450 / 9460-9475

Fill (TD ?)

Then determine if there is a reasonable possi-bility of solving the problem with availablesensors. For instance:

The well is producing above the bubblepoint (down hole) and downhole waterproduction is greater than 10% of the to-tal downhole flow.

D. 6. 2 Running the jobThe second step starts with gathering all therequired data.

Calibrate the tools

Maintain depth control Record data optically and magnetically

D . 6. 3 Interpreting the dataChoose a Single or Biphasic interpretationmodel. Select Computer interpretation ormanual. In both cases the general equations arethe same.

Qh = Yh Qt - Yh (1 - Yh) Vs AQl = Qt - Qh

Qt - Total flowrate

Qh - Heavy phase flowrate

Ql - Light phase flowrate

Yh - Heavy phase holdup (decimal percentby volume)

Vs - Velocity of the light phase relative tothe heavy phase

A - Cross-sectional area

Finally produce the answer (see Figure D4).


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Fig. D4: The result of a production log interpretation


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D . 7 PRODUCTION LOGGINGOPERATIONS

Production logging sensors are available in

many configurations depending on their in-tended use.

Communication between the operating com-pany and the service company is very impor-tant for successful production logging. In anyform of well servicing, good communicationsare wise; but, in production logging, gooddialogue is critical to solving production prob-lems. It is also essential for acquiring goodbase data to more accurately monitor well per-formance and to solve future production prob-lems.

Although there are many types of sensors, thisdoes not necessarily imply that several tripsinto the well will be needed to solve a particu-lar problem. Acquisition of the various formsof data can often be accomplished with one tripinto the well by multiplexing the signals fromthe combined tool string. In addition to rigtime savings and convenience, the reducednumber of trips into the hole can produce lessdisturbance of the production profile as a resultof fewer pressure releases with the surface

pressure control equipment; this helps assurethat all the sensors are logging the flow condi-tions with simultaneous measurements.

D.7.1 Depth Control

Casing Collar Locator SectionFigure D5 shows a combination tool. The toolhas several production logging sensors and acasing collar locator section. As with mosttools run in casing, it is very important thatcasing collars be recorded. Collars are the

only positive depth control link between theproduction logging sensors and the formationstrata.

Gamma Ray LogThe other half of depth control is a gamma raylog run in casing simultaneously with a casingcollar log. The gamma ray in casing is depthmatched to the openhole logs; therefore, thecasing collars that were recorded simultane-ously will be on depth, or correctly depthmatched, relative to the openhole logs. Any

subsequent services run in casing with a casingcollar locator that is depth-matched to the

Gamma ray plus collar log will be on depthwith the openhole logs.

Flowmeter

Casing CollarLocator

Gamma Ray

Fig. D5: Standard tool string showing the casing collarlocator and gamma ray

This procedure is necessary for the depth

measurement accuracy required for perforat-ing, plugs, packers, etc. If cement evaluationis run, a gamma ray and collar locator are usu-ally combined with the cement evaluation tool,typically a sonic device, to acquire depth con-trol data simultaneously with cement informa-tion. These logs are not absolutely essential ifthe production logging tool string contains agamma ray section; however, the gamma ray -collar log is usually run for perforating accu-racy far in advance of the decision to run pro-duction logging tools that may contain agamma ray.


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Production Logging Definition

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