b'Plant & Process | Engineer InnovationHPV 1 OUT OF SERVICEHIGHPOINTVENTGAS GRAVITY SECTION 1 P 1= P 0- H STA (HPV ON) WELL HEAD GAS FILLEDHPV 2 OUT OF SERVICEP 1= P 0+ H STA (HPV OFF)WATER CUP 1GRAVITY SECTION 2TANKH STA DEPTH GAS FILLEDCUP 2 DEPTHP 0Figure 3: Gas bubble at pipeline high point Figure 4: Downhill pipeline schematicHPVs out of service system start up. All PC pumps willservice (Scenario B). Note the hydraulic operate at their pre-set flow rate for amodel in figure 6 only represents considerable time period in order removeScenario B (HPVs out of service). sufficient water from the well to cause the water level to drop just above thePressure results for Wellheads WH5 and coal seam. WH7 are shown in figure 8. How to identify disrupted gravity flowSimilar to the earlier downhill pipeline sectionsdemonstration model, a significant The first simulation run of a completeincrease in backpressure occurs when model is required to identify anycritical HPVs are out of service. This is disrupted gravity flow sections in thecaused by pushing gas bubbles trapped water gathering network. This task isin disrupted gravity flow sections through accomplished by operating thethe downstream cup. unmodified model in no vaporization mode where water can sustain negativeAs demonstrated in figure 8, adopting pressures. Following completion of thisScenario B with critical HPVs out of simulation the nodal pressure results atservice will always result in a more system high points will need to beconservative approach when identifying interrogated. Disrupted gravity flowa safe MAOP.sections can be identified where the nodal pressure at the upstream highOptimization of pipeline diameterspoint is shown to be below 95 kPa.The water gathering system hydraulic model shown in figure 6 including the How to determine a safe maximumdisrupted gravity flow functionality is allowable operating Pressure ready now for further system It can be assumed that HPVs will normallyoptimization work. The modified function in good working order andhydraulic model may be run through hence will ensure relatively lowmultiple simulations by varying maximum allowable operating pressuresimportant system parameters such as (MAOPs). However, with critical HPVs outpipeline diameters and thus allows for of service as shown in Fig.4 HPVs out ofchecking and optimizing wellhead Service, modeling results will always leadbackpressures and the resulting pipe to more conservative MAOPs. Followingsection pressure ratings.this important acknowledgment, the hydraulic model in figure 6 has beenNote that Simcenter Flomaster software, modified by adding the disrupted gravitywhile in dynamic simulation mode, will flow functionality.complete an analysis of an average size gathering system in a matter of a few Results for HPV venting scenarios A & B minutes. This functionally offers fast For comparative purposes, twowhat-if system checks and enables the simulations have been performed, onedesigner to carry out multiple with HPVs working correctly (Scenario A)optimization runs in a short space of and the other with HPVs being out oftime, thus helping him to identify the 51'