Ans. As a data engineer I have multiple responsibilities. My first and foremost duty, after rigging up the unit, is to ensure that mudlogging unit is running smoothly, recording all the data accurately. To do this I have to calibrate and sometimes troubleshoot sensors. Carry out interpretation of data to identify presence of hydrocarbons, optimize mud hydraulics for better ROP and estimate formation pressure to recommend proper mud weight. My job also requires to prepare daily, weekly and final reports and logs for the client.
Ans. Many parameters such as WOB, RPM, Flow Rate, mud hydraulics, MW and Bit Size do effect rate of penetration.
Ans. 1. ROP 2. Hole Size 3. Flow Rate 4. Degasser Efficiency 5. Differential pressure 6. Surface losses. Increasing first four parameters will tend to increase gas readings; while increasing the last two parameters will tend to decrease gas readings.
Ans. Shales have extremely low permeabilities and usually low porosities; as a result, small amount of fluid contained in them does not flow into wellbore. However, in an overpressure zone shale behaves differently: it produces cavings and may cause tight hole if shale is plastic in nature.
Ans. As heat flows from center of the earth to surface of the earth, the geothermal gradient increases with depth almost at constant rate but if an overpressure zone is encountered the geothermal gradient increase at a faster rate than in normal pressure zone. The reason for that is that overpressure zones are under-compacted (more porous), therefore they contain more water. As water is bad conductor of heat it mostly retains the heat instead of passing all of it upward. This is why, the temperature gradient increases at a faster rate inside over pressure zone. This is also the reason why we encounter a lower than normal temperature gradient (zone of heat starvation) just above the overpressure zone. This layer sometime called seal, is usually compact and hard with negligible porosities and permeabilities.
More over please note, the mud temperature-out-data as recorded by mudlogging unit is affected by a number of factors, therefore it is advisable to be extra careful in tracing geothermal gradient. Perhaps plotting temperature data from MWD tools may yield better results.
Ans. Logical steps usually taken are: First have a look at the sensor for its displacement or physical damage as well as check its response or functionality. If that is OK, check for the integrity of cable and connections. If all things look good so far, check and recalibrate sensor. If the problem still persists call for technical assistance from town, there may be problem with electronic channel or PCB.
Ans. Poor hole condition is indicated by abundant cuttings and cavings on shakers, high ECD, High torque, drag and overpull on connections.
In case of differential stuck up (which happens when string gets pushed to the wall of a highly permeable but depleted reservoir) circulation is possible. While in mechanical stuck up (where hole has packed off) circulation is usually not possible, nor we can much rotate or move pipe up and down.
Ans. Main purposes of optimizing mud hydraulics are to improve penetration rate, to avoid build up of cuttings inside the annulus, to efficiently use rig energy and avoid undue stress on circulatory system.
6 ½” holes are usually drilled at deeper depths where the formations are very compact and hard; therefore, the focus is to use maximum hydraulic energy at the bit (by selecting smaller nozzles to get high jet velocities) in order to increase ROP. This strategy is not applied, while drilling 17 ½” hole where formations are usually soft and ROP is naturally fast. In this stage concern is to optimize annular flow rate to remove large amounts of cuttings being generated, efficiently, without seriously eroding the open hole section. The idea is to avoid build-up of cuttings in the annulus and resulting problems.
Ans. Increasing trends of ROP and total gas. Appearance of connection gas, appearance of shale cavings and sometimes high torque and drag on connection. Bear in mind one parameter alone should not be taken as a serious indicator of overpressure zone.
Ans. A chromatograph contains usually two spring shaped aluminum tubes called columns, which are usually filled with micro-beads of silica. These silica beads are tightly packed in such a way that a low permeability or a tortuous path is created for the gases to pass through. Therefore, lighter gases like C1, C2 move ahead followed by heavier gases like C3, C4 and C5. Thus, the gas mixture is broken down into its components.