Investigation of The Effect of Temperature and Contamination on Properties of Saturated Salt-Base mud

The most difficult challenge that can be encountered when drilling a salt section is the difficulty of controlling the change in drilling fluid properties. In addition, the challenging geological environment was encountered. , creep behavior, slim hole drilling in salt formation have a few traits: high soluble, wash out salt section (1). The treatment did by using drilling mud that inhibits changes and is resistant to contaminants. Sodium chloride and potassium chloride brine were used to create a new mud for discussing this research, following up on changes in the properties of the new mud, simulating the conditions of Salt section (12.25'' hole) in the Noor oil field. Moreover, In this investigation studied the effect of temperature and contaminants such as salt, shale and anhydrite on new mud properties (Rheological properties, Filtration, PH with Different concentrations of Kcl & Nacl. The results indicate that the dissolution of salt formation decreases with increasing KCl concentration up to 5% for saturating NaCl salt. This reduces the contaminant impact and increases the stability of mud characteristics.


Introduction:
The first rule in drilling operations must be to study expected drilling problems before making the decision to drill in order to reduce drilling time and costs.
No well is drilled without problems; most of these problems suspend the drilling operations.
Thus, understanding problems and analysis causes help us to avoid problems or reduce the risk of problems, there are many factors have to be considered in planning the well to avoid drilling problems. Subsurface pressure, lithology type (pore pressure, facture pressure, overburden pressure), depth, temperature, location, etc. [1] During drilling operations, one or more of several factors can cause wellbore instability. This instability can manifest itself as caving, a tight hole, or hole erosion. Poor hole cleaning is one of the consequences, which can also lead to packing off, stuck pipe, and ultimately sidetracks. Other consequences include inefficient perforating, poor mud condition, difficulties running casing in and out of the hole, and poor quality cementing and logs. [2] Before action can be taken to improve stability, it is of the utmost relevance that the problem formations and the mechanisms of instability be located. Once the causes are understood, it is possible to make an informed decision about how well planning, drilling procedures, and drilling fluid formulas might be improved to reduce problems and costs. The effect of temperature on salt solubility makes it difficult to maintain such a supersaturated system. [3] The main objective of this study is to investigate the problems of drilling of abnormal salt section in Noor field and proposed a treatment; the current method is to analyze lithology, salt compositions, and detect overpressure zones, followed by an experimental investigation of the effects of lithology contamination (salt, anhydrite, and shale) on mixed salt mud system.

Analysis of chemical components of salt formation.
According to laboratory Analysis of core of salt in lower Fars, the result of analysis shown in Table (1).

Mud Materials
Bentonite should have been pre-hydrated in drill water (freshwater) with chlorides that had been treated with soda ash to reduce free calcium to 200 mg/l. This ensures that the Pre-Hydrated Bentonite yields properly and avoids overuse of the product and additional costs. After adding the Bentonite, the pH should be adjusted to 10.0 with Caustic soda to ensure that enough Bentonite can be added to the original make up water. Before dilution or use, this process should be pre-hydrated for at least 8 hours with the agitators running, Table (2).

The laboratory Apparatus.
Various laboratory instruments [6] for determining rheological properties, fluid loss, and density. Figures (2) through (5) depict these apparatuses. All of these tests were conducted at the Maysan Oil Company's laboratory.  While yield point decreases with saturated salt mud, it rises gradually with the addition of KCl until 7 % yield point remains the same at both temperatures, as depicted in Figure (7).

Effect contaminators on Saturated salt muds.
In the following sections, the effect of contaminants such as salt, anhydrite, and shale on the rheological properties of saturated salt muds will be discussed.

Saturated salt mud +5%Kcl
Due to its high resistance to contamination, saturated salt mud +5% Kcl samples behave slightly differently from those of other types; however, there are no significant changes in the viscosity of the plastic observed in Figure (12).  To understand this phenomenon of rheological parameter effects (PV, Yp) for the saturated salt mud and KCl concentrations, this effect was attributed to the dispersive effect of salt, which can be either physical (by increasing the distance between particles) or chemical (by altering particle surface charge in such a way that particles repel each other).

Rheological models
The Average Absolute Percentage Error method was used to determine best rheological model that fit the saturated salt muds. For these saturated salt muds, the best model can be shown in Table (3), where it has the closest value to one. The Bingham Plastic model is nearest model to samples of drilling fluids as shown in Figure   (14).

Filtration
Filtration rate affects the stability of the wellbore walls, which are subject to softening and degradation by aqueous filtrate. [7] Salt saturated with or without KCl used to examine the impacts of contaminants on Filtration,

Density
Density is particularly significant when drilling abnormal pressure, the fluid must be able to carry the mud weight necessary to control the well, and circulation, surge, and swab pressures must not be excessive. [8] Equivalent mud weight affects density, therefore salt drilling is the most challenging. A high pore pressure salt layer and easy sticking and overflow are seen in the third section (12 1/4") of the pipe. High mud density is needed for abnormal high-pressure section to balance formation pressure; however high density will increase the risk of lost circulation.
During the drilling process, care must be taken to avoid the well kick and leaks. Therefore, the recommended mud density is 2.21 to 2.25 g/cm3. To avoid drilling sticking, reaming should be done on a regular basis.  7-In the salt section, a salt-saturated mud solution with 26% NaCl and 5% KCL will be used to inhibit shale and get the necessary mud weight with the least particles. This will make it easy to run the 9 5/8" casing and cement it without any problems.
8-The optimum mud density of saturated salt mud is (2.21-2.25) gm/cc. 9-It is important to use a PH meter during the drilling salt section to avoid over treatment of caustic soda. The pH will be maintained at the 9-to-10 range; it will be regulated using caustic soda. This improves polymer performance and reduces clay dispersion.
10-Using a 5 percent KCL concentration with saturated salt mud is optimul for mud enhancement and improving saturated salt mud performance.