Wireline

High deviation angles (above 60°) may cause excessive drag or torque while drilling, and will also make it difficult to later service the well with standard wireline tools. 

To derive a reservoir geological model various methods and techniques are employed mainly the analysis of core material, wireline logs, high resolution seismic and outcrop studies. These data gathering techniques are further discussed in Sections 5.3 and 2.2. 

The gradients may be caloulated from surface fluid densities, or may be directly measured by downhole pressure measurements using the repeat formation testing tool (RFT). The interfaces predicted can be used to confirm wireline measurements of fluid contact. 

A hole section which has been cored will subsequently be logged using wireline tools (see later in this section). A gamma ray (GR) measurement will be taken from the core itself, thus allowing calibration of wireline logs with core data. 

The sidewall sampling tool (Sl/VS) can be used to obtain small plugs (2 cm diameter, 5 cm length, often less) directly from the borehole wall. The tool is run on wireline after the hole has been drilled. Some 20 to 30 individual bullets are fired from each gun (Fig. 5.35) at different depths. The hollow bullet will penetrate the formation and a rock sample will be trapped inside the steel cylinder. By pulling the tool upwards, wires connected to the gun pull the bullet and sample from the borehole wall. 

In a more recent development a new wireline tool has been developed that actually drills a plug out of the borehole wall. With sidewall coring (Fig. 5.36) some the main disadvantages of the SWS tool are mitigated, in particular the crushing of the sample. Up to 20 samples can be individually cut and are stored in a container inside the tool. 

Figure 5.37 depicts the basic set up of a wireline logging operation. A sonde is lowered downhole after the drill string has been removed. The sonde is connected via an insulated and reinforced electrical cable to a winch unit at the surface. At a speed of about 600m per hour the cable Is spooled upward and the sonde continuously records formation properties like natural gamma ray radiation, formation resistivity or formation density. The measured data is sent through the cable and is recorded and processed in a sophisticated logging unita the surface. Offshore, this unit will be located in a cabin, while on land it is truck mounted. In either situation data can be transmitted in real time via satellite to company headquarters if required. 

One method of sampling reservoir fluids and taking formation pressures under reservoir conditions in open hole is by using a wireline formation tester. A number of wireline logging companies provide such a tool under the names such as RFT (repeat formation tester) and FMT (formation multi tester), so called because they can take a series of pressure samples in the same logging run. A newer version of the tool is called a modular dynamic tester or MDT (Schlumberger tool), shown in Figure 3.8. 

Perhaps the greatest stimulus for the development of such tools has been the proliferation of high angle wells in which deviation surveys are difficult and wireline logging services are impossible (without some sort of pipe conveyance system), and where MWD logging can minimise formation damage by reducing openhole exposure times. 

Data transmission rate per foot is a function of both pulse frequency and rate of penetration. Sensors acquire and transmit data samples at fixed time intervals and therefore the sampling per foot is a function of rate of penetration. Current tools allow a real time sampling and transmission rate similar to wireline tools as long as the penetration rate does not exceed about 100 ft/h. If drilling progresses faster or if there are significant variations in penetration rate, resampling by depth as opposed to time intervals may be required. 

The purpose of the well completion is to provide a safe conduit for fluid flow from the reservoir to the flowline. The perforations in the casing are typically achieved by running a perforating gun into the well on electrical wireline. The gun is loaded with a charge which, when detonated, fires a high velocity jet through the casing and on into the formation for a distance of around 15-30 cm. In this way communication between the wellbore and the reservoir is established. Wells are commonly perforated after the completion has been installed and pressure tested. 

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. 

When only small amounts of sand, wax or scale are experienced the situation can often be contained using wireline bailers and scrapers, run as part of a well maintenance programme. 

Cement is then placed across the open perforations and partially squeezed Into the formation to seal off all production zones. Depending on the well configuration it is normal to set a series of cement and wireline plugs in both the liner and production casing (see Figure 16.2), to a depth level with the top of cement behind the production casing. 

Kick Alert 1067. Horizontal Drilling, Geosteering 1070. Comparison of LWD Logs with Wireline Logs 1077. Comparison of MWD Data with Other Drilling Data 1078. 

To determine (approximately) the desirable ton-miles before the first cutoff on a new line, draw a vertical line from the derrick height to the wireline size used. Project this line horizontally to the ton-mile figure given for the type of drilling encountered in the area. Subsequent cutoffs should be made at 100 ton-miles less than those indicated for iVs-in. and smaller lines, and at 200 ton-miles less than I A-in. and 1%-in. lines. 

Wireline Core Barrel Systems. The wireline system can be used for continuous drilling or coring operations. The inner barrel or the drill plug center of the core bit can be dropped from the surface and retrieved without pulling the entire drill string. 

The kick-off procedure required numerous single-shot runs to start the deviation in the correct direction. Since, during this phase, the drillpipe was not rotating a steering tool was developed to be lowered on an electric wireline instead of the single shot. The measurements were then made while drilling. 

Figure 4-216 shows the typical operation of a steering tool for orienting the drill bit. The electric wireline goes through a circulating head located on top... 

The arrangement of Figure 4-218 is common to all directional tools based on the earth s magnetic field for orientation MWD tools or wireline logging tools. 

The steering tools have practically been abandoned and replaced by MWD systems, mostly because of the electric wireline. However, the high data rate of the electric wireline (20-30 kbits/s) compared to the low data rate of the MWD systems (1-10 bits/s) make the wireline tools still useful for scientific work. 

A steering tool is normally used during drilling with a mud motor and is connected to the surface with an electric wireline. The sensing devices shown in Figure 4-232 are also used in most MWD mud pulse systems. The coordinates... 

Total Gamma Rays. Total gamma ray logs have been run on electric wireline since 1940. The sondes are rather small in diameter (1.5 to 4 in. or 37 to 100 mm). 

The MWD total gamma ray tools cannot be calibrated in the standard pit, since they are too large. Their calibration in API units is difficult because it varies with the spectral content of the radiation. By spectral matching the MWD logs can be made to closely resemble the wireline logs. The logs which were recorded by the MWD companies in counts per second (cps) are now recorded in API units. 

Another difference between the wireline logs and the MWD logs is the logging speed. With a wireline, the sonde is pulled out at a speed of 500 to 2,000 ft/min (150 to 600 m/min). The time constant used to optimize the effect of the statistical variations of the radioactivity emission, varied from 2 to 6 s. Consequently, the log values are somewhat distorted and inaccurate. 

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