The function of wellhead equipment is to hang the oil pipe and seal the annular space of oil jacket. The basic parts of wellhead equipment are tubing head (casing tee or cross), tubing tee and sealing box. In addition, it is composed of production valve, back pressure valve, vent sampling valve, oil jacket connecting valve, etc., and is equipped with oil pipe and casing pressure gauge to observe the oil casing pressure.

1、 Function of Christmas tree

Wellhead equipment, commonly known as "Christmas tree", is an important and common equipment for oil, gas and water wells, and is the main equipment for controlling and regulating oil well production. Its main functions are:

(1) Hang the tubing and support the weight of all tubing strings in the well;

(2) Seal the annular space between oil and casing to control casing gas;

(3) Control and regulate the production of oil wells;

(4) Take oil, casing pressure data, test, wax removal and other daily management;

(5) Ensure the smooth progress of downhole operations such as well flushing, sand flushing, acidification and fracturing.

Figure 1-1 shows the composition of wellhead Christmas tree.

图1-1 型采油树组成示意图

1-测试阀门；2-左右阀门；3-卡箍；4-油管四通；5-总阀门；6-上法兰；7-套管四通；8-下法兰；9-左右套管阀门；10-油管挂顶丝

二、采油树的类型

采油树分两大类，即老式采油树和采油树。老式采油树指20世纪60年代的大隆（仿大罗马）、荣丰（仿小罗马）、良工（仿苏）等采油树。采油树指我国自己设计制造的大庆150、大庆160微型、胜251、胜II型等采油树。

三、采油树的结构

以国产采油树为例，各零部件有采油树套管四通、左右套管阀门、油管头、油管四通、总阀门、左右阀门、测试阀门或清蜡阀门（封井器）、油管挂顶丝、卡箍、钢圈及其他附件组成。

四、采油树的连接方式

采油树连接方式主要有以下五种：

（1）卡箍连接：采油树各组成部件之间的连接均是以卡箍为主，如大庆150II、胜261微型、胜254等采油树；

（2）螺纹连接：采油树各组成部件之间的连接均是以螺纹为主，如大庆150、胜251等采油树；

（3）铁箍连接：采油树各组成部件之间的连接均是以铁箍为主，如胜I型、胜II型等采油树；

（4）法兰连接：采油树各组成部件之间的连接均是以法兰为主，如上海大隆、荣丰、良工等采油树；

（5）卡箍法兰连接：采油树各组成部件之间的连接均是以卡箍与法兰为主，如原CY250等采油树。