APLIACICON PRACTICA DE RECOMENDACIONES DEL ESTUDIO DE GEOMECANICA by yn5404w

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									   COMPARATIVE ANALYSIS OF EQUIVALENT MUD WEIGHT FROM AN
            ADVANCED HYDRAULICS SIMULATOR AND PWD TOOLS
Authors: Christian Ferreira – Blass Molina – Halliburton


Abstract


Hole cleaning is one of the main factors to the success of drilling of horizontal
and highly deviated wells. This is a key factor to take into account primarily in
angle construction sections and sections with angles between 40 and 90
degrees.


Simulating drilling parameters during the planning stage allows the operator to
anticipate drilling bottomhole pressures (BHP) that are measured by pressure
while drilling (PWD) tools. Through careful analysis of these pressures, problems
related to inadequate hole cleaning can be promptly identified, especially in
sections with angles above 40 degrees. Improper hole cleaning will immediately
show an abnormal increase in pressure values registered by PWDs.


Simulating parameters such as rate of penetration (ROP), pump rates, rotating
and sliding drilling times, connection times, average drilling cuttings size and hole
angles can allow the accurate prediction of BHP while drilling. In this way the
necessary corrective measures can be taken to help ensure the operation is free
of problems associated with hole cleaning.


This document validates BHP values predicted by the simulator compared with
the actual values obtained with PWD tools at different depths and hole
conditions. Once simulator values have been accepted, the same process is
used to determine the expected pressure window registered by PWDs under
optimum hole cleaning conditions. Any abnormal upward deviation in the
pressure values measured by the PWD is potentially related to inadequate hole
cleaning.
Introduction
Six horizontal wells have been drilled during the present campaign in Block 16 in
Ecuador. Information from PWD tools and an advanced hydraulics simulator has
been compared from the fifth well, where a PWD tool was run. A comparison was
made between the actual pressure values presented as equivalent mud weight in
the annulus registered by the PWD tool and the predicted equivalent mud
weights obtained by the simulator considering the annular cuttings load,
connection times, sliding and rotation times, and hole angles. This information is
used to optimize the drilling design for the future wells, and to predict expected
drilling near bit pressures to be measured by PWD tools, and to identify any
deviation of the normal pressure trend that would indicate poor hole cleaning.


Being the 8 1/2” hole section of the angle construction section, usually a 30%
sliding and 70% rotating drilling operation is performed. It is clear that hole
cleaning is a big challenge during this interval. Drillstring rotation has been
identified as one of the main assisting factors in hole cleaning while drilling this
hole section.


As a complementary hole cleaning action, a sweep plan was simulated to
improve drilling fluid cuttings carrying capacity and to prevent cuttings beds
formation.


The main objective of the simulation process was to determine the best
combination of drilling parameters to maintain appropriate hole cleaning and to
calculate the expected EMW for correlation with the EMW registered by PWD
tools. The results given by the advanced hydraulics simulator show cuttings
loading as one of the main factors to consider when evaluating hole cleaning.
Experience shows that annular cuttings load values over 3% represent poor hole
cleaning conditions.   Cuttings loading has a direct effect on equivalent mud
weights registered in the annular section.
Drilling of this hole section is very critical since the formations involved are very
dissimilar with intercalations of clays, shale, depleted sands, and limestone. Mud
chemical properties and the mud density window had to be carefully defined to
prevent hole instability problems. The field crew has to be alert to identify any
instability signals that appear in the drilling parameters or in the appearance of
the drill cuttings. This observation is critical to differentiate hole instability
problems and hole cleaning problems which can have common indicators in the
drilling parameters such as torque and drag.


Data Comparison


For this study, comprehensive hydraulics modeling was performed each 100 feet
while drilling the section and the results of equivalent mud weights are shown
considering the annulus loaded with drilled cuttings and without cuttings that
represents hole clean conditions. The calculated results from the advanced
hydraulics simulator and the actual EMW values registered by the PWD tool were
correlated. The EMW values from both sources and the difference between them
are shown in Table 1.


As can be seen in Table 1, the EMW accuracy obtained with the hydraulics
simulator and its correlation with actual values registered with the PWD tool are
remarkable. It is important to highlight that the difference shown in the last
column of the table is between the EMW values registered by the PWD and the
EMW values calculated by the simulator including cuttings loading which is the
real situation while drilling. The EMW without cuttings values are given as a
reference and should be the minimum EMW to be registered by the PWD tool if
the hole is free of drilling cuttings.
Table 1. PWD and Hydraulics Simulator Equivalent Mud Weights Data Comparison

          APWD Data                    Hydraulics Simulator Data

                                        EMW W/O          EMW With
Depth     EMW                   MW                                   Difference
                                         Cuttings         Cuttings

 8683     10.55                  10        10.61           10.63        0.08
 8789     10.74                  10        10.61           10.79        0.05
 8886      10.7                  10        10.61            10.8        0.1
 8989     10.73                  10        10.61           10.79        0.06
 9086     10.81                  10        10.62           10.83        0.02
 9193     10.94                  10        10.72           10.92       -0.02
 9296     10.98                  10        10.72           10.93       -0.05
 9396     10.94                  10        10.73           10.93       -0.01
 9489     10.99                  10        10.73           11.04        0.05
 9586     11.06                  10        10.73           11.07        0.01
 9689     11.21                  10        10.74           11.203      -0.007
 9789     11.23                  10        11.04           11.28        0.05
 9889     11.31                  10        11.05           11.29       -0.02
10030     11.48                  10        11.12           11.35       -0.13
10060     11.68   MWD Failure   10.1       11.43           11.56       -0.12
10162     11.56                 10.1       11.44           11.58        0.02
10260     11.59                 10.1       11.45           11.59         0
10362     11.55                 10.1       11.57            11.8        0.25
10390     12.02   MWD Failure   10.1       11.57           11.75       -0.27
10490     11.71                 10.1       11.58           11.82        0.11
10590     11.74                 10.1       11.58           11.82        0.08


Some of the parameters included in the simulator calculation process are shown
below:
        Pump rates
        Hole angle and well geometry
        Sliding and rotating drilling times and ROPs.
        Drilling fluid properties
        Circulating and connection times
        Cuttings size and density
        Pipe rotation
A graphical representation of the values obtained is presented in Fig. 1. It is
important to highlight the similarity of the results for EMW with cuttings calculated
in the hydraulics simulator with the values registered by the PWD tool. The trend
of the lines is very similar with main differences registered at two MWD failure
events. The red line represents the expected EMW values considering that
drilling fluid is completely free of cuttings or the hole is totally clean.



                                                   APWD and Hydraulics Simulator EMW values
               8250

                                                                                                                  APWD Data
               8500

                                                                                                                  EMW W/O Cuttings
               8750
                                  MW: 10.0 ppg Dev 33                                                             EMW With Cuttings
               9000
                                                                                                                  MW
               9250
                                  Napo formation 82 dev.
 Depth, Feet




               9500


               9750
                                  Tena Formation                                                                          MWD
                                                                                                                          Failures
               10000


               10250
                                      Basal Tena Formation 81 dev.
               10500                  MW: 10.1 ppg

               10750


               11000
                                         10.2




                                                                     10.8




                                                                                                        11.6




                                                                                                               11.8
                                                   10.4




                                                           10.6




                                                                                        11.2




                                                                                                 11.4




                                                                                                                                      12.2
                       9.8




                             10




                                                                               11




                                                                                                                           12

                                                                        Equivalent Mud Weight, ppg


Fig. 1 - EMW comparison between simulator results and registered values from PWD.



Drilling Optimization Plan
Below are shown several recommendations being included in the drilling fluids
plan for the wells to be drilled.
                      The hydraulics simulator should be used to find the optimum combination
                       of pump rates, ROP, pipe rotation, connection and circulation times,
                       sliding and drilling times, and drilling fluid properties to help ensure
                       effective hole cleaning.
      Validate planning results from the hydraulics simulator every 100 feet to
       re-calculate the equivalent mud weights to be expected with actual field
       parameters and to correlate these results with EMW values registered by
       PWD tools. Any deviation of the expected trends should be carefully
       considered and evaluated. Higher EMW trends registered by PWD could
       be an indicator of poor hole cleaning.
      Define carefully the drilling plan per well considering preventive actions to
       avoid hole cleaning issues. This plan will include drilling parameters
       optimization by reducing sliding times, increasing pump rates and
       maximizing rotation of the drillstring as much as possible.
      Continue obtaining actual near bit pressure values while drilling and
       continue correlating these values with results calculated by simulator to
       narrow the EMW expected window under optimum hole cleaning
       conditions and define corrective hole cleaning action plan if needed.
      Keep good communication and understanding of drilling parameters
       among all members of drilling team to take promptly action when
       parameters indicate potential hole cleaning issues.
      Use the hydraulics simulator to predict annular cuttings load. This cuttings
       load has a direct effect on equivalent mud densities. Cuttings load values
       over 3% usually represent poor hole cleaning conditions.


Simulation Parameters and Results
The figures below represent part of the drilling optimization process. These
figures show the effect of changing drilling parameters on annular cuttings load
and equivalent mud weights. The main objective in this simulation is to find the
best combination of drilling parameters to optimize drilling times and hole
cleaning.


Besides the well geometry parameters and drilling fluid rheological properties,
drilling parameters considered for this example are as follows:
      Mud weight 10 ppg.
      ROP: rotating @ 50 rpm: 60 feet/hr - - Sliding: 30 feet/hr
      Circulating time before connection 5 minutes rotating pipe @ 50 rpm
      Connection time 5 minutes.
      Average cuttings size: 0.2 inches.


Using these parameters, the simulation process was performed considering
several changes in drilling parameters to evaluate circulating time requirements,
rpm, changes in mud properties, or corrective sweeps plan to help ensure good
hole cleaning.


Several figures show part of this drilling optimization study, where it is possible to
evaluate the effect of drilling parameters like pipe rotation and sliding versus
drilling times. It is important to highlight that a very comprehensive combination
of drilling parameters was also evaluated but are not included due to space
constraints.


The following four figures are shown to describe the effect on annular cuttings
load created by changing pipe rotation speeds and sliding/rotation drilling times.


      Drilling 75% Rotating and 25% sliding – Fig. 2
      Drilling 100% Sliding - Fig. 3
      Drilling 100% Rotating at 50 rpm – Fig. 4
      Drilling 100% Rotating at 100 rpm – Fig. 5
Fig 2 – Annular cuttings load of 2.094% and the corresponding EMW of 11.339 ppg and the
EMW value without cuttings load (hole clean) of 11.115 ppg.



On the first column of the figure are shown the cuttings loads by hole section
according to its geometry and hole angle. The second column shows average
anular velocity for the fluid according to pump rate and hole section geometry.
The third column shows the hole angle per section. The fourth column shows the
calculated EMW trends with and without cuttings loads and the last column
shows a graphical representation of the hole geometry. The upper right corner
shows some of the parameters used for the drilling simulation and the calculated
annular cuttings load percentage.
Fig 3 – Situation considering an ROP of 30 ft/hr 100% sliding.



On the top right corner appears in red an annular cuttings load of 5.394%. This
value indicates that if the well is drilled with these drilling parameters, poor hole
cleaning will be experienced. It is important to see also the effect of the high
annular cuttings load on EMW: 11.616 ppg versus the EMW of 11.313 ppg
shown in the previous figure considering 75% rotating and 25% sliding.
Fig 4 – Situation considering an ROP of 60 ft/hr 100% rotating pipe at 50 rpm.



On the top right corner appears an annular cuttings load of 1.798%. This value
indicates that if the well is drilled with these drilling parameters, good hole
cleaning will be experienced. It is important to see also the effect of the low
annular cuttings load on EMW: 11.305 ppg versus the EMW of 11.115 ppg
calculated if the annulus is free of cuttings.
Fig 5 – Situation considering an ROP of 60 ft/hr 100% rotating pipe at 100 rpm.



On the top right corner appears an annular cuttings load of 0.785%. This value
indicates that if well is drilled with these drilling parameters, very good hole
cleaning will be experienced. It is important to see also the effect of this very low
annular cuttings load on EMW: 11.209 ppg versus the EMW of 11.115 ppg
calculated if the annulus is free of cuttings.


Conclusions
      Besides drilling fluid properties pump rates and hole geometry, other
       drilling parameters should be included in the drilling optimization process.
       These parameters include: ROP, pipe rotation speeds, rotation vs sliding
       times and cuttings size.
      Correlating EMW values with measured PWD values can allow prompt
       and correct decisions to help ensure good hole cleaning for drilling high
       angle sections.
   Drilling on paper using the advanced hydraulics simulator should be
    performed considering all possible scenarios to be faced during the actual
    drilling operation. All the time expended on drilling optimization planning
    will provide a better understanding of the actual well operation and will
    help facilitate accurate decisions.
   While drilling high angle hole sections, as sliding time increases, the
    tendency for cuttings beds formation increases and the annular cuttings
    load increases as well. In other words, as sliding time increases the
    efficiency of the hole cleaning has a significant reduction.
   The hydraulics simulator should be used to find the optimum combination
    of pump rates, rates of penetration, pipe rotation, connection and
    circulation times, sliding and drilling times, and drilling fluid properties to
    help ensure optimum hole cleaning.
   Drilling optimization results from the hydraulics simulator should be
    continuously re-calculated and correlated with actual EMW values
    registered by PWD tools. Any deviation of the expected trends should be
    carefully considered and evaluated. Higher EMW trends registered by
    PWD tools could be an indicator of poor hole cleaning.
   In reviewing the actual drilling operation data and correlating them with
    hydraulics simulator modeling results, the EMW base line for optimum
    hole cleaning should be achieved for each particular well situation.

								
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