Dipmeter log

To find the hole orientation and dip direction of the formation beds. 91. Repeat formation tester

Measures formation pressure and obtains fluid samples. 92. Formation micro-scanner/fullbore Formation Microlmager

Provides a detailed image of the borehole wall.

The following guidelines should be considered when wireline logging. These are general guidelines and thus any experience of a specific nature should take precedence:

93. Hole conditioning:

Run a wiper trip. Work any tight hole.

Circulate the cuttings from the hole with the drill bit just off bottom. Condition the mud to run electric logs.

Use pipe spinner to come out of the hole. Strap out of the hole prior to all logging jobs. 94. Mud sampling:

A circulated mud sample from the well must be obtained. The sample must be taken from the flowline before any water or other additives are placed in the mud and saved in a CLEAN container for the logger. This sample should be used for determining the resistivity of the mud.

Have the logger run a filtration test on the mud from this sample.

Use the filtrate and mud cake from this test, and have their resistivities measured. DO NOT PERMIT THE USE OF CORRELATIONS FOR THIS INFORMATION.

Keep mud samples from freezing.

95. Prior to any wireline logging job a pre-job/safety meeting must be held. The programme should be discussed by all key personnel.

96. Tools containing radio-active sources may be run on the first logging run in open hole if the hole conditions are favourable.

97. Dummy trips should be made as, and when hole conditions dictate.

98. The rigging up/down must be supervised by the Company Representative. 99. A down-hole tension tool is to be included in every logging suite. If a logging tool

becomes stuck it can be used to establish whether the tool or the cable is stuck.

100.All radioactive tools must be transported in "clearly marked" special containers. It must be clearly indicated whether they contain radioactive material or if the container is empty. 101.Ensure that sufficient cable on the drum is available to log to the required depth. The

logging company must submit the log-in cable history log upon request.

102.Depth discrepancies between driller’s depth and logger’s depth of up to +/-2 m per 1000 m are acceptable; discrepancies in excess of this should be investigated and reported to the area petrophysicist.

103.Stuck logging tools

Stuck logging tools must be fished using the strip over/reverse strip technique. If a radio-active source becomes stuck it must be treated as an emergency incident. No attempt is to be made to break the cable at the weak point unless instructed to do so by the Company Representative. Do not exceed a line tension of 50% of the weak point breaking strength.

104.Logging programs and requirements

For an example of the Well Logging Programme see Form 7.1 at the back of this section. 105.Log Quality Control Check List (Form 7.2).

106.Service Company Performance Evaluation (Form 7.3). 107.Field Data Transmittal (Form 7.4).

108.Open-hole logging tool types

109.Formation Resistivity

Sedimentary rocks, when dry, will not conduct electricity. However, current will flow through the interstitial water made conductive by salts in solution. The most common salt ions are sodium (Na++), calcium (Ca++), Chlorine (Cl-) and sulphate (SO4-). If an

electric logging tool emits an electric field, these ions will move carrying the current through the solution. If everything else is constant, the greater the concentration of ions the lower the resistivity of the formation water, and of course the formation. The

presence of shale in the formation will also contribute to the electrical conductivity of the formation. The conduction of electricity in shale is an ion exchange process between charged particles of clay. The net effect of shale depends on the amount, type and distribution of the shale, and the nature and relative amount of the formation water. More than one resistivity measurement is needed because of the effects of invasion. The flushed zone resistivity (Rxo) next to the borehole is higher than the resistivity of the

uninvaded zone (Ro), because the mud filtrate in the flushed zone usually has a higher resistivity than the formation water resistivity (Rw) in the uninvaded portion of the

formation. Occasionally, mud filtrate resistivity is less than the formation water resistivity. This may occur when a well is drilled with salt muds or at very shallow depths where the formation water is more likely to be fresh (less salty, higher resistivity).Effects of invasion cause the resistivity to vary close to the borehole. Sometimes it is high; at other times it is low, depending on the resistivity of the mud filtrate, the formation water, the water saturation, and the porosity. The farther the measurement is taken horizontally from the borehole (into the formation) the more nearly it will match the true resistivity of the formation.

In electrical logging practices we measure formation resistivity or specific resistance which is a formation characteristic where:

R = rA

L

R = resistivity in ohms-metre2/metre r = resistance

A = area in metre2 L = length in metres 110.Resistivity Logs

Resistivity logs are used to measure the resistivity of the formation. Resistivity logs only work in uncased holes:

high resistivity = rock , oil, gas, drinking water low resistivity = shale, salt water

Various types of resistivity logs in use are: 49. Normal Device and Lateral Device:

E Log (Normal Device)

The electric log, or E-log, are mechanically simple but are quite difficult to effectively interpret. A current of constant intensity is passed between electrode A, which is at the logging tool, and electrode B, which is at the surface. The resultant potential difference is measured between electrode M, which is also on the logging tool, and N, which is located at surface. Since the current emitted by A is constant, any variation in the voltage at M will be due to changes in the resistivity of the formations.

The electrodes A and M, on the sonde of the logging tool, are separated by a distance called the spacing. Common spacings are 16" for the short normal, 64" for the

medium normal, and 18'8" for the lateral log.

Usually the greater the distance between electrodes A and M the deeper the tool investigates into the formation. The 16" normal has the shallowest depth of investigation, while the 18'8" lateral log has the deepest depth of investigation. These normal devices are used to read the formation’s apparent resistivity (Ra) or true resistivity (Rt). These tools are especially useful in locating water-oil contacts, water-gas contacts or gas-oil contacts. A lost circulation zone will also be apparent from the reading of the normal device, provided the drilling fluid has a different resistivity than the formation fluids.