Geological Description Part 1

It is very important to understand what geological description used in oil filed business. Hence, I collect the geological description from the book in order to be your reference and you will be able to understand meaning of each photo describing type of rock.

lime stone = Limestone (Ls)

dolomite and shalk = Dolomite&Chalk (Dol & Chk)

chert = Chert (Cht)

Limestones, Dolomite and Chalk are formed from large deposit of calcium carbonate (calcite) and calcium magnesium (dolomite).

gypsum = Gypsum & Anhydrite (Gyp & Anhy)

salt = Salt (Sa)

Gypsum, Anhydrite and Salt are composed of minerals precipitated from solution during evaporation of water.

basement = Basement (Bm)

volcanic = Volcanics (Volc)

Basement and Volcanics are formed from the cooling of molten magma.

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Oil Well Cementing (Purpose and its importance)

Purposes of oil well cementing are as follows:

Zonal Isolation: Isolate hydrocarbon pays, water pays, shale, etc.

Seal off lost circulation zones

Hydraulic Seal: Prevent pressure from the undesirable migration of fluid coming up to surface via annulus between casing and hole.

Protect casing: Cement is a protective sheath around casing.

Hold casing and completion string: Cement supports weight of whole string of casing or completion.

The importance to accomplish the primary oil well cementing is  as follows:

Good reservoir management: Good cement will let engineer design to produce hydrocarbon from reservoirs easier because there is no concern related to cement.

Maximize Reserves: Good cement sheath allows good pay sands to produce as maximum as possible because good sands will stop producing earlier due to water load-up or permeability damage.

Save time and cost: A lot of time and money must be spent to perform remedial cement operation which is cement squeeze job by coiled tubing or Hydraulic Work Over. If primary cement can be accomplished, no more time and money is spent out to do remedial work.

The key factors necessary to ensure a successful primary oil well cement job are as follows:

1. Good information: Related information such as calculated hole diameter, hole volume, depth, etc from related personnel is required in order to design cementing programs.

2. Good cementing design: There is a number of cement purposes such as primary cement, cement squeeze, cement plug. To meet the purpose of each job, cementers must design a cementing program in correct and good way.

3. Good procedures: Clear and concise procedure will lead to good job because cementer and assistants can perform the cementing job correctly, fast, safely.

4. Good equipment and experienced personnel: Experienced staff with good equipment can perform great jobs, no lost time, safe and fast.

5. Good centralizer placement: Centralizers help casing in the center of hole. Casing with good centralizer placement, cement can form properly cement sheath around casing.

Ref books: Cementing Technology Books

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Understand about Friction Pressure Acting (FrP) in Wellbore

The friction pressure is pressure loss when fluid flowing through flowing paths and it acts in opposite direction of fluid flow. The following factors affect the friction pressure:

• Drilling string geometry both inside diameter and outside diameter

• Fluid Properties: Rheology and density

• Geometry of wellbore: hole length, wellbore area and flow area

• Wellbore condition such as packing off, bridging, etc

• Flow Rate

• Pipe movement and pipe rotation

The figure below demonstrates you how the friction act in wellbore.

3.5 friction pressure

Reference book: Well Control Books

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How to Predict Formation Pressure Prior to Drilling

Formation pressure can be predicted from 3 information sources prior to drilling as follows;

1. Seismic Data

Seismic is the way to predict formation types by sending sound waves that penetrate into subsurface structure. Then, sound waves reflected back from formation are recorded as raw data. Geologists are able to predict geological structures and potential pressured zoned by interpreting the sound waves. With current 3D seismic modeling, the pressured zones are accurately predicted.

2. Geological Data

Geological information demonstrates condition that possibly causes abnormal pressure zones. The subsurface structures associated with abnormal pressure characteristics are anticlines, charged zones, depleted zones, faults, massive shale and Salt formations.

Anticlines: Anticlines is the geological structure that looks like a dome. Anticlines with cap rock on top are good geological structure because hydrocarbon can possibly trapped below it. While drilling into top structure of anticlines, abnormal pressured zones are expected.

Charged Zones: Charged zones are shallow formations that have pressure connectivity from abnormal pressure zones below. Because of upward movement of reservoir fluid from deeper zones, charged zones are normally abnormal pressure. Charge zones can occur by nature or man-made. Currently, new geophysical methodologies can be applied for find where the charged zones are prior to drilling.

Depleted Zones: Depleted zones are formations that have less pressure than original formation pressure because some formation fluid has been produced. Using historical data in conjunction with geological techniques can determine where the possibly depleted zones are.

Faults: Because each fault block may has different pressure gradient, while drilling across a fault, drilling problem associated with pressure such as well control problem or lost circulation may possibly happen.

Massive Shale: Shale is non permeable formation therefore it restricts movement of formation fluid. When a lot of overburden formation layers are accumulated over massive shale, shale is compacted and reservoir fluid naturally tries to come out from the pore space. However, shale is impermeable and it does not allowed pore fluid to come out therefore formation pressure caused by formation fluid becomes over pressured.

Salt Formations: There are several parts of the world where pure and thick layers of salt are present. Typically, salt formations are laterally and upwards forced causing salt domes. Because salt is impermeable, it does not allow formation fluid pass through it; therefore, formations below a salt formation are normally abnormal pressure.

3. Historical Data

The historical data from adjacent area is good information for prediction formation pressure. Historical information can be obtained from formation pressure, mud logging reports, drilling reports, drilling fluid reports, Logging While Drilling (LWD), Pressure While Drilling (PWD), etc.
Reference book: Well Control Books

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How to Assess Material Requirements for Drilling Operation

Drilling supervisors must be responsible for assessing material requirements for the drilling operation at a drilling rig. There are several following information that can help to assess material requirement in both short time (less than 48 hrs) and long time (next 3-5 day).

1. Drilling Operation Instruction: The drilling operation instruction is guidance for what operations will be happening in the future. Therefore, it will give people at the rig some ideas regarding what people will be needed.

2. Drilling Operation Meeting: The operation meeting is conducted everyday in order to discuss the forward plan among team members such as drilling supervisors, a drilling contractor and service companies. This meeting helps all parties at the rig to understand what drilling activities will be performed and when the operation requires the material perform jobs.

3. Forward plan sheet: The forward plan sheet contains all actions from demobilization to completion of the drilling program. It assists supervisors on the rig to estimate time for upcoming operations. Mostly, it is utilized for assessing the long time (next 3-5 days) material and people requirement.

4. Area on the rig: Operation supervisors must fully understand about available space of the rig because it is a constraint about how much equipment can be store on the rig. For instant, if the rig has small area, small set of equipment must be frequently ordered. On the other hand, if the rig area is big, a lot of drilling tools can be requested and kept on the rig.

5. Logistics: It is very important to know how the logistics work each area because it will help personnel on the rig know how long the equipment will be transferred from a wear house to a location after issuing the material.

6. Contact Warehouse: After all required materials are assessed, drilling supervisors and a material man must contact a warehouse in order to discuss with them about what the required materials are and when they should be at the rig site.

Normally, material requirement plan must be revised everyday because sometimes drilling operation is not ongoing as plan. Therefore, some equipment must be delayed or some special equipment must be urgently requested for specific drilling operation.

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