GEOCVM
Problems related to wellbore instabilities are a source of non-productive time and lead to substantial cost increments. In order to optimize performance during drilling operations, an important parameter that needs carefully monitoring is the volume of cuttings coming to the surface. The accurate real-time measurement of cuttings flow is therefore essential to correctly evaluate the borehole behavior while drilling, in combination with geo-mechanical borehole stability analysis and other available drilling information and data. Problems of stability or inadequate cleaning of the well from cuttings can cause serious problems on the operations with consequent high impact on total well running costs. By comparing the real volume of the hole versus the theoretical one, the presences of caving or cleaning problems can be monitored. The basic principle is that the measured volume of cuttings should correspond to the theoretical volume of the hole. |  |
This operation is traditionally conducted during post drilling log caliper measurement, however in many cases this can be too late to avert unnecessary costs. Intervening immediately and correcting mud and drilling parameters is therefore vital. The knowledge of the well volume while drilling can be done exclusively with the direct measurement of the quantity of cuttings coming to the surface. Properly processed cuttings weight data, allows the evaluation in real-time of the volume and flow of cuttings retrieved from the wellbore and to correlate it with the drilling events (e.g.: drilling, circulating, tripping in tripping out, BHA drags , BHA over pulls, etc.).
In co-operation with oil major ENI SpA, Geolog has developed and perfected over the years the most efficient method to measure the weight of the cuttings collected at shale shakers during drilling and circulation via its GeoCVM service. A cutting weight machine is installed in front of each shale shaker, and connected to the mud logging data acquisition system.
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A real-time engineering software transforms the weight of cuttings measured at the shale shakers into volume and the results are graphically displayed in real-time on the rig floor to the Oil Company representative officer. The data coming from cutting machines is evaluated both versus depth and versus time in order to obtain the instantaneous picture of wellbore behavior during drilling, tripping and circulating.
This technology finds its major application on deviated/horizontal wells, where it is key to:
- optimising drilling efficiency
- preventing getting stuck
- modifying RIH and or POH procedures,
- improving cementation when electrical logging caliper is not available to estimate cement volume
- modifying mud programs and measuring the effectiveness of the change.
In case of non-linearity between theoretical and measured bore-hole volume, Geolog’s specialists, together with the Oil Company representative, mud engineer and drilling contractor representatives are able to correct mud properties and drilling parameters while drilling in order to improve the situation and avoid serious consequences. As a result, the drilling crew know exactly what is happening down hole, e.g. when caving occurs or when cuttings remain in the hole and additional circulation is required. Furthermore, additional information is provided to the mud engineer to better evaluate the mud efficiency. If, for example, the system shows that the volume of cuttings retrieved while drilling a deviated well is much less than the theoretical one, this could be related to the poor cleaning efficiency of the mud system. A poor cuttings recovery during circulation at the end of a bit run would aggravate such a situation. In order to solve this problem, changes to the mud should be considered. Moreover, to avoid pack-offs and related over pulls while tripping out, a viscous pill should be run.
The mechanism of the system is deeply analysed in the paper “OMC 2005 Offshore Mediterranean conference” available on this web site upon request.
Compared to similar services offered by some of our Mud Logging competitors, Geolog’s service has significant advantages in the measurement of the cutting weight, the reliability of the system, the reduced dimensions and encumbrance of the equipment and in the determination of cutting properties and calculation of borehole volume. This maximises efficiency and reliability and provides information on real borehole volume while drilling.
Real-time software transforms the weight of cuttings measured at the shale shakers into volume and the results are graphically displayed in real-time on the rig floor to the Oil Company representative officer.
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