Best Practices and Guidelines for Drilling to the Top of Salt Formation

Although it may not always be possible to meet all the strategic criteria, some guidelines for drilling above and into the top of salt are as follows:

1)       Selection of surface location:

a)       Deeper salt beds exhibit a higher creep rate due to the weight of overlying sediments and higher temperatures.

b)       If the geological and well profile complexities make it feasible, select a surface location that minimizes the sediment thickness above the salt.

2)       Entry point profile:

a)       Choose a salt entry location with the flattest salt formation profile.

b)       The seam at the salt diapers has more stress, and hence, entering it at an angle poses higher formation instability.

3)       Preparedness for potential losses:

a)       A dirty salt layer and rubble zone are commonly encountered immediately above a salt dome.

b)       This zone could be more stressed and fragmented, posing a higher risk of lost circulation.

c)       All emergency preparations should be made to handle potential losses while entering a salt zone

d)       Prepare and discuss a pre-drill loss mitigation road map with the team.

e)       Pre-plan formulations and preparation to mix pills for combating moderate to severe levels of losses.

4)       Bottom hole assembly:

a)       The top of salt is usually a heterogeneous layer before the well enters cleaner, homogeneous salt. Hence, drilling through it could result in a higher level of vibrations.

b)       A well-stabilized BHA should be used to drill to the top of the salt. An unstable BHA can lead to pronounced vibration at the top of the salt, potentially damaging the downhole tools.

c)       Plan to deploy downhole tools to pump light, moderate, and heavy LCM pills.

5)       Directional planning:

a)       Carrying out directional work in the salt should be minimized.

b)       Consider building the angle before entering the salt if deviating the well at a shallow depth.

6)       Casing point:

a)       Drilling through the salt formation usually requires higher mud weight to avoid salt creep.

b)       Setting the casing before entering salt will leave the seam at the transition zone open, which is usually prone to losses and could cause complications while drilling the creeping salt with higher mud weight.

c)       It is recommended to isolate the shallow, weaker formation before drilling the salt zone and set the casing well into the salt. This strategy ensures that the casing covers "dirty salt," inclusions, and other troublesome geologic features behind the pipe and achieves a good shoe.

7)       Real-time measurement tools:

a)       The Bottom Hole Assembly (BHA) should include LWD tools of GR/RES/DT to get real-time data. Real-time formation data helps assess the changes downhole and decision on the casing point.

b) In certain cases, a thin layer of salt could be inter-bedded in the transition zone, which could wrongly indicate that the well has entered the salt. Including a ‘Seismic While Drilling’ tool in the bottom hole assembly could help identify the top of the salt while drilling and ensure that the casing is not set too soon.