Introduction• The purpose of this section is to provide an interpretation guide for ECD responses. Some of the known, clearly identifiable, and repeatable signatures of ECD changes have been put into tables along with secondary or confirming indications, such as those seen in surface measurements. • Downhole annular pressure interpretation is an evolving technique. All possible downhole events have not yet been observed. Nonetheless, certain clearly identifiable and repeatable signatures can be used to diagnose problems. Combining the information you get from downhole annular pressure logs with other drilling parameters creates an overall assessment – the big picture – and drilling problems can be detected before they get severe. In order to maintain a healthy drilling environment, we have to put emphasis on anticipation and prevention rather than reaction and cure. • Logs of downhole annular pressure and other drilling performance parameters show a process – a process that is evolving with time. The evolution of the log in real-time must be monitored as downhole conditions are dynamic, and timely decisions are essential. Delay or indecision can lead to serious risk and added cost. • Since ECD is a drilling parameter and not a formation parameter, ECD should be plotted on a timebased log along with relevant surface parameters. Small changes can tell us a lot about the downhole environment, and it is therefore crucial that ECD is being plotted on a very fine scale. • Stable or slight decrease • Circulation while pulling pipe if greater than pipe displacement will eliminate swab effect. inadequate hole fill – monitor active system . • Can only monitor with MWD if flow above minimum operating level. • Pressure max/min values will be pulsed to surface. NB. • Mud Losses – record trip tank volume against pipe displacement Downward Pipe Movement .ECD Interpretation Guide OPERATION / HAZARD ECD/PRESSURE CHANGE ADDITIONAL OBSERVATIONS Running In / Downward Pipe Movement .surging (Flow off) Pressure Increase (memory only) To check flow off pressure values in “real-time”.surging (Flow on) • Monitor active pit system for mud losses Pulling Pipe swabbing (Flow on) • Mud gains. • Stop pipe movement • Wait 30 seconds to allow system to stabilize • Break circulation following pump start procedures • Stage pumps gently to MWD operating flow limit for operation. • This is a high risk operation when close to balance. • Pressure Increase • Mud flow will enhance the increase in ECD when moving pipe downwards. Rapid pipe acceleration will cause large pressure peak. If nozzles plugged or float in the string the pressure increase is greater. The pressure peak will be greater for cold muds that have gelled i. after a trip • ECD should be equal to the static mud weight • The downhole MW is very often different to the MW measured at surface. • Stage pumps gently to MWD operating flow limit for operation. Especially oil-based muds tend to have a lower MW downhole than what is measured at surface conditions. • NB. inadequate hole fill – monitor trip tank Pump Start (Mud Gelation) • Increase in Standpipe Pressure above normal circulation levels • Monitor active pit system for mud losses •No flow or SPP Making a Connection . • Sudden Increase Possible • Dependant on how quick the pumps are kicked in and fluid rheology. ADDITIONAL OBSERVATIONS • Mud gains. If nozzles plugged or float in the string the pressure decrease is greater.ECD Interpretation Guide OPERATION / HAZARD Pulling Pipe swabbing (Flow off) ECD/PRESSURE CHANGE Pressure Decrease (memory only) To check flow off pressure values in “real-time”. • Stop pipe movement • Wait 30 seconds to allow system to stabilize • Break circulation following pump start procedures. due to pressure and temperature effects. • Pressure max/min values will be pulsed to surface.e. Especially oil-based muds tend to have a lower MW downhole than what is measured at surface conditions. ADDITIONAL OBSERVATIONS • Mud gains. after a trip • ECD should be equal to the static mud weight • The downhole MW is very often different to the MW measured at surface.e. due to pressure and temperature effects. inadequate hole fill – monitor trip tank Pump Start (Mud Gelation) • Sudden Increase Possible • Dependant on how quick the pumps are kicked in and fluid rheology. If nozzles plugged or float in the string the pressure decrease is greater. NB. The pressure peak will be greater for cold muds that have gelled i. • Refer also to: Pulling Pipe/Downward Pipe Movement/Pump Start • Increase in Standpipe Pressure above normal circulation levels • Monitor active pit system for mud losses • No flow or SPP Making a Connection .ECD Interpretation Guide OPERATION / HAZARD Pulling Pipe swabbing (Flow off) ECD/PRESSURE CHANGE Pressure Decrease To check flow off pressure values in “real-time”. • Stage pumps gently to MWD operating flow limit for operation. • Pressure max/min values will be pulsed to surface. • Stop pipe movement • Wait 30 seconds to allow system to stabilize • Break circulation following pump start procedures. building up on the low side of the hole. causing the ECD to decrease. • Once rotary drilling continues pipe rotation lifts cuttings into suspension and ECD increases as cuttings are transported beyond horizontal section.ECD Interpretation Guide OPERATION / HAZARD Circulate after a Connection (Deviated wells only) Rotation after Steered Interval (Deviated wells only) ECD/PRESSURE CHANGE • Gradual Increase then Level Off • Cuttings may fall out of suspension when the pumps are off. Picked up when circulation/rotation starts after connection • Gradual Increase then Level Off • Cuttings transport may become inefficient while drilling without rotation and cuttings beds form. If near plugging you might get pressure surge spikes. • Reduced quantity of cuttings at surface • monitor cuttings at shakers • monitor mud in active ADDITIONAL OBSERVATIONS • SPP may show a gradual increase before levelling off • Increased torque and drag since last rotary interval • Increase in cuttings at shakers (after lag time) String Rotation Cuttings Bed Formation (Poor hole cleaning in deviated wells) . • Slow Gradual Increase • Substantial cuttings bed develop causes constriction in the annulus increasing frictional pressure loss and therefore ECD increases. • Step Increase in Pressure for initial RPM increase then gradual increase with RPM • Decrease • Cuttings falling out of suspension. • Increasing torque/drag • Overpull increasing • Lower than expected ROP due to poor WOB transfer to the bit. • Overpull above normal drag • SPP displaying gradual cycle of increase or decrease depending on location of light/heavy mud. sudden large increase if complete annular pack off.ECD Interpretation Guide OPERATION / HAZARD Pack Off in Annulus (above Sensor) ECD/PRESSURE CHANGE • Erratic Pressure causing ECD Peaks ADDITIONAL OBSERVATIONS • Erratic variations in SPP – may not be obvious if motor in string unless pack off becomes severe • Increased rotary torque becoming erratic • Overpull increasing • Increase in SPP. • Mud loss if particularly dense interval occurs Pack Off in Annulus also bit/stabilizer balling (below sensor) • No change/drop to static MW • Sudden increase if pack-off passes sensor Barite Sag • Slow fluctuations in circulating density (ECD) • Decrease in Static Mud Density . • Increase (memory only as pumps off) • If the well is shut in and the gas influx migrates up the annulus Liquid Influx (SWF) • Decrease • If the influx is above the sensor and is lighter than the drilling fluid.ECD Interpretation Guide OPERATION / HAZARD Gas Influx (SWF) ECD/PRESSURE CHANGE • Decrease • If the influx is above the sensor and has started to expand in the annulus and the well has not been shut in. • Increase • If the influx has the same density as the drilling fluid or if the influx is accompanied by solids • Decrease in SPP • Increase in mud flow out • Increase in active volume • Plan response if shallow water flow expected. ADDITIONAL OBSERVATIONS • Decrease in SPP • Increase in mud flow out • Increase in active volume .